Patent Publication Number: US-2005120231-A1

Title: Method and system for controlling network connection, and computer product

Description:
BACKGROUND OF THE INVENTION  
      1) Field of the Invention  
      The present invention relates to a technology for controlling network connections so as to prevent computers on the network form viral infections.  
      2) Description of the Related Art  
      It is common to exchange data using recording mediums such as FDs (flexible disks) and CD-Ra (CD recordable), or via networks.  
      It is also common to perform access restriction in which access is allowed to only certain computers. For example, the access restriction is performed using a switch that connects the computer to the network or using a radio network access point to connect computers to network according to the standards such as IEEE802.1x.  
      However, the access restriction is not enough to protect a computer from computer viruses; because, the computer of the authenticated user could be infected.  
      Virus infection protective methods are known. In the technology disclosed in Japanese Patent Application Laid-Open No. H7B81980, for example, virus inspection information of a computer is checked before making communications with that computer, and communications are started only when it can be confirmed that it is safe to perform communication with that computer. However, there is a problem that it is necessary to be apply the method to all the computers that are connected via a network.  
      Accordingly, it has been an important subject to develop a practical method that enables not only to prevent virus infection between a user&#39;s own computer and its partner computer, but also to prevent virus infection to other computers connected to network.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to solve at least the problems in the conventional technology.  
      A network connection control program according to an aspect of the present invention is run on a computer and relays communications by specified computers via a network, and controls connections of the specified computers to the network. The network connection control program makes the computer execute the steps including accepting connection control information about connection control generated on the basis of security countermeasure condition information about computer security countermeasure conditions of specified computers; and controlling the connections of the specified computers to the network on the basis of the connection control information accepted at the accepting step.  
      A network connection control program according to another aspect of the present invention is run on a computer and relays communications by specified computers via a network, and controls connections of the specified computers to the network. The network connection control program makes the computer execute the steps including accepting security countermeasure condition information about computer security countermeasure conditions of the specified computers; judging whether the security countermeasure conditions accepted are sufficient; and controlling the connections of the specified computers to the network on the basis of a result obtained at the judging step.  
      A network connection control method according to still another aspect of the present invention is a method of relaying communications by specified computers via a network, and controlling connections of the specified computers to the network. The network connection control method includes accepting connection control information about connection control generated on the basis of security countermeasure condition information about computer security countermeasure conditions of specified computers; and controlling the connections of the specified computers to the network on the basis of the connection control information accepted at the accepting.  
      A network connection control method according to still another aspect of the present invention is a method of relaying communications by specified computers via a network, and controlling connections of the specified computers to the network. The network connection control method includes accepting security countermeasure condition information about computer security countermeasure conditions of the specified computers; judging whether the security countermeasure conditions accepted are sufficient; and controlling the connections of the specified computers to the network on the basis of a result obtained at the judging.  
      A network connection control device according to still another aspect of the present invention relays communications by specified computers via a network, and controls connections of the specified computers to the network. The network connection control device includes an accepting unit that accepts connection control information about connection control generated on the basis of security countermeasure condition information about computer security countermeasure conditions of specified computers; and a controlling unit that controls the connections of the specified computers to the network on the basis of the connection control information accepted by the accepting unit.  
      A network connection control device according to still another aspect of the present invention relays communications by specified computers via a network, and controls connections of the specified computers to the network. The network connection control device includes an accepting unit that accepts security countermeasure condition information about computer security countermeasure conditions of the specified computers; a judging unit that judges whether the security countermeasure conditions accepted are sufficient; and a controlling unit that controls the connections of the specified computers to the network on the basis of a result obtained by the judging unit.  
      The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a functional block diagram of the network connection control system according to a first embodiment;  
       FIG. 2  is an example of security countermeasure level data  50  that the terminal device  10  sends;  
       FIG. 3  is an example of security countermeasure level transfer data  60  that the switch  20  sends;  
       FIG. 4  is an example of the port control table  22  shown in  FIG. 1 ;  
       FIG. 5  is an example of the judgment result data  70  sent to the control server device  30 ;  
       FIG. 6  is an example of the connection condition data  32  shown in  FIG. 1 ;  
       FIG. 7A  is a flow chart ( 1 ) of the process procedure of the connection control process that the switch  20  according to the first embodiment conducts;  
       FIG. 7B  is a flow chart ( 2 ) of the process procedure of the connection control process that the switch  20  according to the first embodiment conducts;  
       FIG. 8  is a flow chart of the process procedure of the connection propriety judgment process that the control server device  30  according to the first embodiment conducts;  
       FIG. 9  is a functional block diagram of a network connection control system according to a second embodiment;  
       FIG. 10  is an example of the port control table  92  shown in  FIG. 9 ;  
       FIG. 11  is an example of the judgment result data  140  sent to the control server device  100 ;  
       FIG. 12  is an example of the connection condition data  102  shown in  FIG. 9   
       FIG. 13A  is a flow chart ( 1 ) of the process procedure of the connection control process that the switch  90  according to the second embodiment conducts;  
       FIG. 13B  is a flow chart ( 2 ) of the process procedure of the connection control process that the switch  90  according to the second embodiment conducts;  
       FIG. 14  is a flow chart of the process procedure of the switching destination VLAN judgment process that the control server device  100  according to the second embodiment performs;  
       FIG. 15  is a functional block diagram of a network connection control system according to a third embodiment;  
       FIG. 16  is an example of the port control table  162  shown in  FIG. 15 ;  
       FIG. 17  is an example of the connection condition data  172  shown in  FIG. 15 ;  
       FIG. 18  is a functional block diagram of a network connection control system according to a fourth embodiment;  
       FIG. 19  is a functional block diagram of a network connection control system according to a fifth embodiment;  
       FIG. 20  is an example of security countermeasure level data  310  that the terminal device  260  sends;  
       FIG. 21  is an example of security countermeasure level transfer data  320  that the switch  270  sends;  
       FIG. 22A  is a flow chart ( 1 ) of the process procedure of the connection control process that the switch  270  according to the fifth embodiment conducts;  
       FIG. 22B  is a flow chart ( 2 ) of the process procedure of the connection control process that the switch  270  according to the fifth embodiment conducts;  
       FIG. 23  is a flow chart of the process procedure of the user authentication process that the authentication server device  280  according to the fifth embodiment performs;  
       FIG. 24  is a functional block diagram of a network connection control system according to a sixth embodiment;  
       FIG. 25  is a functional block diagram of a network connection control system according to a seventh embodiment; and  
       FIG. 26  is a block diagram showing the structure of a computer  500  in a modified example of the embodiment. 
    
    
     DETAILED DESCRIPTION  
      Exemplary embodiments of a network connection control program, a network connection control method, and a network connection control system according to the present invention are explained below by referring to the accompanying drawings. A switch is assumed here as an example of the network connection control system.  
      The switch is a network device to relay data received from computers, and send data to a port connected to a destination computer via network. However, the present invention is not limited to the switch, but may be applied also to any network device such as a radio network access point having similar functions in the same manners.  
      The structure of a network connection control system according to a first embodiment is explained hereinafter.  FIG. 1  is a functional block diagram of the network connection control system according to a first embodiment.  
      In this network connection control system, a terminal device  10  and a control server device  30  are connected with each other via a switch  20 . Moreover, the switch  20  is connected to a network  40  to which plural terminal devices and server devices (not shown) are connected.  
      The terminal device  10  is a terminal device such as a personal computer to which various application software programs are installed. The terminal device  10  includes a communication processing unit  11 , a security countermeasure level data acquisition unit  12  and a control unit  13 .  
      The communication processing unit  11  is a communication processing unit that carries out communications with other connected terminal devices, server devices, the switch  20  and the like via the network. The security countermeasure level data acquisition unit  12  is an acquisition unit that acquires the computer virus countermeasure conditions of the terminal device  10  as security countermeasure level data. The acquired security countermeasure level data is sent by the communication processing unit  11  to the switch  20 .  
      By the way, the connection of a terminal device not having the security countermeasure level data acquisition unit  12  to the network  40  is rejected; therefore, a software program that realizes the functions of the security countermeasure level data acquisition unit  12  must be installed in such a terminal device.  
       FIG. 2  is an example of security countermeasure level data  50  that the terminal device  10  sends. The security countermeasure level data  50  includes information pieces of OS (Operating System) type, OS update time and date, anti virus software program version, anti virus software engine version, and anti virus software pattern version.  
      The OS type is the information about the type of an OS installed in the terminal device  10 . The OS update time and date is the information about the time and date of an update of the OS. The anti virus software program version is the information about the version of the anti virus software program installed in the terminal device  10 . The anti virus software engine version is the information about the version of the engine of the anti virus software program that detects and deletes a virus. The anti virus software pattern version is the information about the version of the virus detection pattern to which the anti virus engine refers.  
      The security countermeasure level data is made as one including the above respective items, but the security countermeasure level data is not limited to this, but may further include information pieces about the installation conditions of various application software programs and the like. Thereby, the system can cope with even a case wherein for example an application software program that is likely to be infected by computer viruses is installed in the terminal device  10 .  
      Back to the explanation of  FIG. 1 , the control unit  13  is a control unit that entirely controls the terminal device  10 , and sends and receives data with the respective functional units.  
      The switch  20  is a network device that relays data received from the terminal device  10 , and sends data to a port to which a terminal device or a server device as a destination is connected via the network  40 .  
      The switch  20  not only relays data, but also, when it receives the security countermeasure level data  50  from the terminal device  10 , it transfers the received security countermeasure level data  50  to the control server device  30 . The control server device  30  judges whether or not to allow the terminal device  10  to send the data via the network  40 , on the basis of the sent security countermeasure level data  50 .  
      Then, the switch  20  receives the judgment result of connection propriety sent by the control server device  30 , and memorizes the connection propriety information in correspondence with the port to which the terminal device  10  is connected. When the data is sent by the terminal device  10 , on the basis of the memorized connection propriety information, the switch  20  carries out a process to connect the terminal device  10  to the network  40  or a process to reject the connection.  
      The switch  20  includes a communication processing unit  21 , a port control table  22 , a connection control unit  23 , and a control unit  24 . The communication processing unit  21  is a communication processing unit that communicates with the terminal device  10  and the control server device  30 . The communication processing unit  21  also carries out a process to relay communications with a terminal device or a server device connected to the terminal device  10  and the network  40 .  
      Concretely, when the data accepted from the terminal device  10  is the security countermeasure level data  50 , this communication processing unit  21  generates security countermeasure level transfer data wherein the information of the port that has accepted the data is added to the security countermeasure level data  50 , and transfers that data to the control server device  30 . While, when the data accepted from the terminal device  10  is other data than the security countermeasure level data  50 , the communication processing unit  21  transfers that data to the connection control unit  23 .  
       FIG. 3  is an example of security countermeasure level transfer data  60  that the switch  20  sends. As shown in  FIG. 3 , this security countermeasure level transfer data  60  includes information pieces of identification information, OS (Operating System) type, OS update time and date, anti virus software program version, anti virus software engine version, and anti virus software pattern version.  
      The identification information is an identification number that identifies the port at which the switch  20  accepts the data from the terminal device  10 , while the OS (Operating System) type, the OS update time and date, the anti virus software program version, the anti virus software engine version, and the anti virus software pattern version are the respective information pieces included in the security countermeasure level data  50 .  
      Back to the explanation of  FIG. 1 , the port control table  22  is a table wherein the information about the communication permission or rejection set to each communication port of the switch  20  is registered.  FIG. 4  is an example of the port control table  22  shown in  FIG. 1 .  
      As shown in  FIG. 4 , in this port control table  22 , respective information pieces of port number, port status, and identification information are registered. The port number is an identification number that identifies the respective ports that the switch  20  has. The port status is information showing connection acceptance or rejection set to ports to which respective terminal devices are connected. By the way, in the default status before the control server device  30  judges connection acceptance or rejection to the network  40  of the terminal device  10 , the port status is set to “connection rejection”.  
      The identification information is information that identifies the port at which the security countermeasure level data  50  is accepted from the terminal device  10 . The identification information is generated at the moment when the security countermeasure level data  50  is accepted from the terminal device  10 , and is sent together with the security countermeasure level data  50  to the control server device  30 .  
      The connection control unit  23  is a control unit that refers to the port control table  22 , when it receives data from the terminal device  10  to a terminal device or a server device connected to the network  40 , and thereby judges the connection propriety to the network  40 .  
      Concretely, the connection control unit  23  rejects the connection to the network  40  when the port status corresponding to the port that has received data is set to “connection rejection” in the port control table  22 , while it permits the connection to the network  40 , and carries out a process to send data to the port to which the terminal device or the server device at communication destination when the port status is set to “connection permission”.  
      The connection control unit  23  sends the security countermeasure level transfer data  60  wherein identification information is added to the security countermeasure level data  50 , to the control server device  30 , and when it receives judgment result data showing the identification information and connection acceptance or rejection judgment result from the control server device  30  in response thereto, it carries out a process to set the port status of the port corresponding to the identification information concerned in the port control table  22  to “connection rejection” or “connection permission”.  
       FIG. 5  is an example of the judgment result data  70  that is sent to the control server device  30 . As shown in  FIG. 5 , this judgment result data  70  includes identification information and judgment result information. The identification information is the information that identifies ports of the switch  20 , and the judgment result is the information showing connection acceptance or rejection judged by the control server device  30 .  
      Back to the explanation of  FIG. 1 , the control unit  24  is a control unit that entirely controls the terminal device  20 , and sends and receives data with the respective functional units.  
      The control server device  30  is a unit that receives the security countermeasure level transfer data  60  from the switch  20 , and judges whether or not to permit the connection of the terminal device  10  to the network  40 , on the basis of the security countermeasure level data  50  included in the security countermeasure level transfer data  60 .  
      The control server device  30  includes a communication processing unit  31 , connection condition data  32 , a connection propriety judgment unit  33  and a control unit  34 . The communication processing unit  31  is a communication processing unit that communicates with the switch  20 , and receives the security countermeasure level transfer data  60  sent from the switch  20 , and sends out judgment result data  70  to the switch  20 .  
      The connection condition data  32  is data that is referred to at the moment of judgment whether or not to connect the terminal device  10  to the network  40 , and memorizes the conditions to decide connection propriety.  
       FIG. 6  is an example of the connection condition data  32  shown in  FIG. 1 . As shown in  FIG. 6 , in this connection condition data  32 , respective information pieces of security countermeasure level and judgment conditions are registered.  
      The security countermeasure level includes respective items selected to judge the conditions of computer virus countermeasures, which correspond to the respective items included in the security countermeasure level data  50  that is sent by the terminal device  10 . The judgment conditions are conditions that the respective items registered in the security countermeasure level should satisfy.  
      By the way, herein, the connection condition data  32  is to be memorized in the control server device  30 , while in place of this, inquiries may be made to a server device that an anti virus software vender or the like holds, and the connection condition data memorized in the server device may be referred to.  
      Back to the explanation of  FIG. 1 , the connection propriety judgment unit  33  judges whether the respective items of the security countermeasure level data  50  included in the security countermeasure level transfer data  60  that the connection processing unit  31  has received satisfy the respective judgment conditions memorized in the connection condition data  32  or not, and generates the judgment result data  70  shown in  FIG. 5 , and carries out a process to send the judgment result data via the communication processing unit  31  to the switch  20 .  
      The control unit  34  is a control unit that entirely controls the control server device  30 , and sends and receives data with the respective functional units.  
      The process procedure of the connection control process that the switch  20  according to the first embodiment performs is explained hereinafter.  FIG. 7A  and  FIG. 7B  are flow charts ( 1 ) and ( 2 ) respectively showing the process procedure of the connection control process that the switch  20  according to the first embodiment conducts.  
      As shown in  FIG. 7A , first, the communication processing unit  21  of the switch  20  receives data (step S 101 ). The communication processing unit  21  judges whether the data has be received at the port at the side of the terminal device  10  or not (step S 102 ), and when the data has been received at the port at the side of the terminal device  10  (step S 102 , Yes), the communication processing unit  21  checks whether the received data is the security countermeasure level data  50  or not (step S 103 ).  
      When the received data is not the security countermeasure level data  50  (step S 103 , No), the connection control unit  23  confirms the port status corresponding to the port that has received the data in reference to the port control table  22  (step S 104 ), and checks whether the port status is “connection rejection” or not (step S 105 ).  
      When the port status is not “connection rejection” (step S 105 , No), the connection control unit  23  sends the data received from the terminal device  10  to a terminal device or a server device at destination via the network  40  (step S 106 ), and completes the connection control process. When the port status is “connection rejection” (step S 105 , Yes), the connection control unit  23  deletes the data received from the terminal device  10  (step S 110 ), and completes the connection control process.  
      In the step S 103 , when the data received from the terminal device  10  is the security countermeasure level data  50  (step S 103 , Yes), the communication processing unit  21  generates identification information that identifies the port that has received the data (step S 107 ), and transfers the security countermeasure level transfer data  60  wherein the identification information is added to the security countermeasure level data  50  to the control server device  30  (step S 108 ).  
      Then, the communication processing unit  21  stores the generated identification information into the port control table  22  in correspondence to the port that has received the data (step S 109 ), and completes the connection control process.  
      In the step S 102 , when the data has not been received at the port at the side of the terminal device  10 , but received at the port at the side of the control server device  30  (step S 102 , No), as shown in  FIG. 7B , the communication processing unit  21  checks whether the received data is the judgment result data  70  sent in response to the security countermeasure level transfer data  60  sent to the control server device  30  or not (step S 111 ).  
      When the received data is the judgment result data  70  (step S 111 , Yes), the connection control unit  23  searches for a port with identification information that corresponds to the identification information included in the judgment result data  70  from the port control table  22  (step S 112 ), and checks whether there is a port whose identification information corresponds to the identification information included in the judgment result data or not (step S 113 ).  
      When there is a port whose identification information corresponds to the identification information included in the judgment result data (step S 113 , Yes), the connection control unit  23  sets the port status “connection permission” or “connection rejection” in correspondence to the port whose identification information corresponds to the identification information included in the judgment result data (step S 114 ), and clears the identification information of the port control table  22  (step S 115 ), and completes the connection control process. When there is not any port whose identification information corresponds to the identification information included in the judgment result data (step S 113 , No), the connection control unit  23  deletes the received judgment result data  70  (step S 116 ), and completes the connection control process.  
      In the step S 111 , when the received data is not the judgment result data  70  (step S 111 , No), the connection control portion  23  confirms the port status of the port corresponding to the destination of the data concerned in the port control table  22  (step S 117 ), and as shown in  FIG. 7A , checks whether the port status is “connection rejection” or not (step S 105 ).  
      When the port status is not “connection rejection” (step S 105 , No), the connection control unit  23  sends the data received from the control server device  30  to the terminal device or server device at destination via the network  40  (step S 106 ), and completes the connection control process. When the port status is “connection rejection” (step S 105 , Yes), the connection control unit  23  deletes the data received from the control server device  30  (step S 110 ), and completes the connection control process.  
      The process procedure of the connection propriety judgment process that the control server device  30  according to the first embodiment performs is explained hereinafter.  FIG. 8  is a flow chart of the process procedure of the connection propriety judgment process that the control server device  30  according to the first embodiment conducts.  
      As shown in  FIG. 8 , first, the communication processing unit  31  of the control server device  30  receives the security countermeasure level transfer data  60  sent by the switch  20  (step S 201 ). The connection propriety judgment unit  33  acquires the connection condition data  32  (step S 202 ), and checks whether the respective items of the security countermeasure level data  50  included in the received security countermeasure level transfer data  60  satisfy the respective conditions of the connection condition data  32  or not (step S 203 ).  
      When the respective items of the security countermeasure level data included in the received security countermeasure level transfer data satisfy the respective conditions of the connection condition data  32  (step S 203 , Yes), the connection propriety judgment unit  33  adds the judgment result of “connection permission” to the identification information and thereby generates the judgment result data  70  (step S 204 ). Then, the communication processing unit  31  sends the judgment result data  70  generated by the connection propriety judgment unit  33  to the switch  20  (step S 205 ).  
      When the respective items of the security countermeasure level data included in the received security countermeasure level transfer data do not satisfy the respective conditions of the connection condition data  32  (step S 203 , No), the connection propriety judgment unit  33  adds the judgment result of “connection rejection” to the identification information and thereby generates the judgment result data  70  (step S 206 ). Then, the communication processing unit  31  sends the judgment result data  70  generated by the connection propriety judgment unit  33  to the switch  20  (step S 205 ).  
      As mentioned above, in the first embodiment, the communication processing unit  21  of the switch  20  receives the connection propriety information of the terminal device  10  to the network  40  judged by the control server device  30  on the basis of the security countermeasure level data  50  of the terminal device  10 , and on the basis of the received information, the communication processing unit  21  controls the connection of the terminal device  10  to the network  40 , accordingly, the first embodiment makes it possible to appropriately prevent a computer virus from infecting from a terminal device  10  whose security countermeasures are insufficient to other terminal devices or server devices connected to the network  40 .  
      By the way, in the first embodiment, when it is judged that the security countermeasures of the terminal device are insufficient, the switch controls the connection of the terminal device to the network, while in place of this, the switch may control the connection to a VLAN (Virtual Local Area Network) wherein a network is logically divided.  
      Concretely, when security countermeasures are insufficient, by restricting the system so that the terminal device can carry out communications only in a VLAN wherein a server device that can update an OS and an anti virus software program is connected, even if the terminal device is infected by a computer virus, the system makes it possible to prevent the infection from spreading over other devices connected to the network. Further, it is possible to prevent the terminal device from being infected by a computer virus from other devices during the terminal device is updating an OS or an anti virus software program. Therefore, in a second embodiment, a case wherein the switch controls the connection to a VLAN is explained hereinafter.  
      In the first place, the structure of a network connection control system according to the second embodiment is explained hereinafter.  FIG. 9  is a functional block diagram of a network connection control system according to the second embodiment. By the way, detailed explanations about the similar functional units to those in the first embodiment shown in  FIG. 1  are omitted hereinafter.  
      As shown in  FIG. 9 , in this network connection control system, a terminal device  80  and a switch  90  are connected with each other, and the switch  90  and a control server device  100  are connected with each other, and a VLAN  110  wherein a network is logically divided, and an update VLAN  120  are connected to the switch  90 .  
      The update VLAN  120  is a VLAN wherein the terminal device  80  is connected to an update server device  130  that can update an OS or an anti virus software program, while the VLAN  110  is a VLAN that is used when the terminal device  80  carries out communications with other terminal device or server device (not shown).  
      The terminal device  80  is a terminal device such as a personal computer to which various application software programs are installed, and a communication processing unit  81 , a security countermeasure level data acquisition unit  82  and a control unit  83  that the terminal device  80  holds have the functions similar to those of the communication processing unit  11 , the security countermeasure level data acquisition unit  12  and the control unit  13  shown in  FIG. 1 .  
      The switch  90  is a network device that relays data received from the terminal device  80 , and sends data to a port of the VLAN  110  or the update VLAN  120  to which a terminal device or a server device as a destination is connected.  
      The switch  90  not only relays data, but also, when it receives the security countermeasure level data similar to that shown in  FIG. 2  from the terminal device  80 , it transfers the received security countermeasure level data to the control server device  30 . The control server device  100  judges the VLAN to which the terminal device  80  should be connected, on the basis of the security countermeasure level data.  
      Then, the switch  90  receives the judgment result sent by the control server device  100 , and memorizes the VALN information in correspondence with the port to which the terminal device  80  is connected. When the data is sent by the terminal device  80 , on the basis of the memorized VLAN information, the switch  90  carries out a process to connect the terminal device  80  to the VLAN  110  or the update VLAN  120  or a process to reject the connection.  
      The switch  90  includes a communication processing unit  91 , a port control table  92 , a connection control unit  93 , and a control unit  94 . The communication processing unit  91  is a communication processing unit that has the functions similar to those of the communication processing unit  21  shown in  FIG. 1 .  
      The port control table  92  is a table wherein information about the VLAN set to the respective communication ports of the switch  90  is registered.  FIG. 10  is an example of the port control table  92  shown in  FIG. 9 .  
      As shown in  FIG. 10 , in this port control table  92 , respective information pieces of port number, port status, and identification information are registered. The port number is an identification number that identifies the respective ports that the switch  90  has. The port status is VLAN information of the connection destination set to ports to which respective terminal devices are connected. By the way, in the default status before the control server device  30  judges the VLAN of the connection destination of the terminal device  80 , the port status is set to “connection rejection”.  
      The identification information is information that identifies the port at which the security countermeasure level data is accepted from the terminal device  80 . The identification information is generated at the moment when the security countermeasure level data is accepted from the terminal device  80 , and is sent together with the security countermeasure level data to the control server device  100 .  
      The connection control unit  93  is a control unit that refers to the port control table  92  when it receives data from the terminal device  80  to a terminal device or a server device connected to the VLAN  110 , and thereby judges the connection propriety to the VLAN  110 .  
      Concretely, the connection control unit  93  permits the connection to the VLAN  110  when the port status corresponding to the port that has received data is set to the VLAN  110  in the port control table  92 , and sends the data to the port corresponding to the VLAN  110 . While, when the port status corresponding to the port that has received the data is set to the update VLAN  120 , the connection control unit rejects the connection to the VLAN  110 , and sets the port so that communications should be made only with the update VLAN  120 .  
      The connection control unit  93  sends the security countermeasure level transfer data wherein identification information is added to the security countermeasure level data, to the control server device  100 , and when it receives the identification information from the control server device  100  and judgment result data showing the judgment result of the VLAN to which the terminal device  80  is connected, in response thereto, it carries out a process to set the port status of the port corresponding to the identification information concerned in the port control table  92 .  
       FIG. 11  is an example of the judgment result data  140  that is sent by the control server device  100 . As shown in  FIG. 11 , this judgment result data  140  includes identification information and switching destination VLAN information. The identification information is the information that identifies ports of the switch  90 , and the switching destination VLAN information is the information of the VLAN to which the terminal device  80  is connected, judged by the control server device  100 .  
      Back to the explanation of  FIG. 9 , the control unit  94  is a control unit that entirely controls the terminal device  90 , and sends and receives data with the respective functional units.  
      The control server device  100  is a server device that receives the security countermeasure level transfer data from the switch  90 , and judges which VLAN the terminal device  80  should be connected to, on the basis of the security countermeasure level data included in the security countermeasure level transfer data.  
      The control server device  100  includes a communication processing unit  101 , connection condition data  102 , a connection destination VLAN judgment unit  103  and a control unit  104 . The communication processing unit  101  is a communication processing unit that communicates with the switch  90 , and receives the security countermeasure level transfer data sent from the switch  90 , and sends out judgment result data  140  to the switch  90 .  
      The connection condition data  102  is data that is referred to at the moment of judgment the VLAN to which the terminal device  80  is connected, and memorizes the conditions to decide the connection destination VLAN.  
       FIG. 12  is an example of the connection condition data  102  shown in  FIG. 9 . As shown in  FIG. 12 , in this connection condition data  102 , respective information pieces of security countermeasure level, judgment conditions, condition dissatisfaction VLAN switching destination information, and condition satisfaction VLAN switching destination information are registered.  
      The security countermeasure level includes respective items selected to judge the conditions of computer virus countermeasures, which correspond to the respective items included in the security countermeasure level data that is sent by the terminal device  80 . The judgment conditions are conditions that the respective items registered in the security countermeasure level should satisfy.  
      The condition dissatisfaction VLAN switching destination information is information of the update VALN  120  that is to be set as the switching destination VLAN, when the respective items included in the security countermeasure level data are not satisfied. The condition satisfaction VLAN switching destination information is information of the VLAN  110  that is to be connected, when the respective items included in the security countermeasure level data are satisfied.  
      Back to the explanation of  FIG. 9 , the connection destination VLAN judgment unit  103  judges whether the respective items of the security countermeasure level data included in the security countermeasure level transfer data that the communication processing unit  101  receives satisfy the respective judgment conditions memorized in the connection condition data  102  or not, and generates the judgment result data  140  shown in  FIG. 11 , and carries out a process to send the judgment result data via the communication processing unit  101  to the switch  90 .  
      The control unit  104  is a control unit that entirely controls the control server device  100 , and sends and receives data with the respective functional units.  
      The process procedure of the connection control process that the switch  90  according to the second embodiment conducts is explained hereinafter.  FIG. 13A  and  FIG. 13B  are flow charts ( 1 ) and ( 2 ) respectively showing the process procedure of the connection control process that the switch  90  according to the second embodiment conducts.  
      As shown in  FIG. 13A , first, the communication processing unit  91  of the switch  90  receives data (step S 301 ). The communication processing unit  91  judges whether the data has been received at the port at the side of the terminal device  80  or not (step S 302 ), and when the data has been received at the port at the side of the terminal device  80  (step S 302 , Yes), the communication processing unit  91  checks whether the received data is the security countermeasure level data or not (step S 303 ).  
      When the received data is not the security countermeasure level data (step S 303 , No), the connection control unit  93  confirms the port status corresponding to the port that has received the data in reference to the port control table  92  (step S 304 ), and checks whether the port status is “connection rejection” or not (step S 305 ).  
      When the port status is not “connection rejection” (step S 305 , No), the connection control unit  93  sends the received data via the VLAN designated in the port control table  92  (step S 306 ), and completes the connection control process. When the port status is “connection rejection” (step S 305 , Yes), the connection control unit  93  deletes the data received from the terminal device  80  (step S 310 ), and completes the connection control process.  
      In the step S 303 , when the data received from the terminal device  80  is the security countermeasure level data (step S 303 , Yes), the communication processing unit  91  generates identification information that identifies the port that has received the data (step S 307 ), and transfers the security countermeasure level transfer data wherein the identification information is added to the security countermeasure level data to the control server device  100  (step S 308 ).  
      Then, the communication processing unit  91  stores the identification information into the port control table  92  in correspondence to the port that has received the data (step S 309 ), and completes the connection control process.  
      In the step S 302 , when the data has not been received at the port at the side of the terminal device  80 , but received at the port at the side of the control server device  100  (step S 302 , No), as shown in  FIG. 13B , the communication processing unit  91  checks whether the received data is the judgment result data  140  that is sent in response to the security countermeasure level transfer data sent to the control server device  100  or not (step S 311 ).  
      When the received data is the judgment result data  140  (step S 311 , Yes), the connection control unit  93  searches for a port having identification information to correspond to the identification information included in the judgment result data  140  from the port control table  92  (step S 312 ), and checks whether there is a port whose identification information corresponds to the identification information included in the judgment result data or not (step S 313 ).  
      When there is a port whose identification information corresponds to the identification information included in the judgment result data (step S 313 , Yes), the connection control unit  93  sets the switching destination VLAN information to the port status in correspondence to the port whose identification information corresponds to the identification information included in the judgment result data (step S 314 ), and clears the identification information of the port control table  92  (step S 315 ), and completes the connection control process. When there is not any port whose identification information corresponds to the identification information included in the judgment result data (step S 313 , No), the connection control unit  93  deletes the received judgment result data  140  (step S 316 ), and completes the connection control process.  
      In the step S 311 , when the received data is not the judgment result data  140  (step S 311 , No), the connection control portion  93  confirms the port status of the port corresponding to the destination of the data concerned in the port control table  92  (step S 317 ), and as shown in  FIG. 13A , checks whether the port status is “connection rejection” or not (step S 305 ).  
      When the port status is not “connection rejection” (step S 305 , No), the connection control unit  93  sends the received data via the VLAN designated by the port control table  92  (step S 306 ), and completes the connection control process. When the port status is “connection rejection” (step S 305 , Yes), the connection control unit  93  deletes the data received from the control server device  100  (step S 310 ), and completes the connection control process.  
      The process procedure of the switching destination VLAN judgment process that the control server device  100  according to the second embodiment performs is explained hereinafter.  FIG. 14  is a flow chart of the process procedure of the switching destination VLAN judgment process that the control server device  100  according to the second embodiment performs.  
      As shown in  FIG. 14 , first, the communication processing unit  101  of the control server device  100  receives the security countermeasure level transfer data that is sent by the switch  90  (step S 401 ). The connection destination VLAN judgment unit  103  acquires the connection condition data  102  (step S 402 ), and checks whether the respective items of the security countermeasure level data included in the received security countermeasure level transfer data satisfy the respective conditions of the connection condition data  102  or not (step S 403 ).  
      When the respective items of the security countermeasure level data included in the received security countermeasure level transfer data satisfy the respective conditions of the connection condition data  102  (step S 403 , Yes), the connection destination VLAN judgment unit  103  adds the condition satisfaction VLAN switching destination information to the identification information and thereby generates judgment result data  140  (step S 404 ). Then, the communication processing unit  101  sends the judgment result data  140  generated by the connection destination VLAN judgment unit  103  to the switch  90  (step S 405 ).  
      When the respective items of the security countermeasure level data included in the received security countermeasure level transfer data do not satisfy the respective conditions of the connection condition data  102  (step S 403 , No), the connection destination VLAN judgment unit  103  adds the condition dissatisfaction VLAN switching destination information to the identification information and thereby generates judgment result data  140  (step S 406 ). Then, the communication processing unit  101  sends the judgment result data  140  generated by the connection destination VLAN judgment unit  103  to the switch  90  (step S 405 ).  
      By the way, in the second embodiment, a case wherein a common update VLAN  120  is allotted to respective terminal devices whose security countermeasures are insufficient, while in place of this, an individual update VLAN may be allotted to each of terminal devices.  
      Further, in combination with the first embodiment, the process to connect the terminal device to the network and the process to reject the connection, and the process to limit the VLAN that permits the connection may be employed in combination.  
      As mentioned above, in the second embodiment, when the network is logically divided as a VLAN, the communication processing unit  91  of the switch  90  receives the information of the VLAN  110  or the update VLAN  120 , to which the terminal device  80  is connected, judged by the control server device  100  on the basis of the security countermeasure level data of the terminal device  80 , and the communication processing unit  93  of the switch  90 , on the basis of the received information, limits the VLAN that permits the terminal device  80  to connect to the VLAN  110  or the update VLAN  120 , accordingly, the second embodiment makes it possible to appropriately prevent a computer virus from infecting from the terminal device  80  whose security countermeasures are insufficient to other terminal devices or server devices connected to the VLAN  110 .  
      By the way, in the second embodiment, the connection destination of the terminal device in the network is limited by designating the VLAN, while in place of this, by designating IP address and port number and the like of a terminal device or a server device at destination with which communications are made, filtering may be made, and thereby the connection of the terminal device to network may be limited.  
      Concretely, when security countermeasures of a terminal device are insufficient, by restricting addresses and port numbers so that the terminal device can carry out communications only with the update server device that can update an OS and an anti virus software program, even if the terminal device is infected by a computer virus, the system makes it possible to prevent the infection from spreading over other devices connected to the network. Therefore, in a third embodiment, a case wherein the switch carries out filtering by use of IP address and thereby controls the connection is explained hereinafter.  
      In the first place, the structure of a network connection control system according to the third embodiment is explained hereinafter.  FIG. 15  is a functional block diagram of a network connection control system according to the third embodiment. By the way, detailed explanations about the functional units similar to those in the first embodiment shown in  FIG. 1  are omitted hereinafter.  
      As shown in  FIG. 15 , in this network connection control system, a terminal device  150  and a switch  160  are connected with each other, and the switch  160  and a control server device  170  are connected with each other, and the switch  160  is connected to a network  180  to which plural terminal devices and server devices (not shown) are connected.  
      The terminal device  150  is a terminal device such as a personal computer to which various application software programs are installed, and a communication processing unit  151 , a security countermeasure level data acquisition unit  152  and a control unit  153  equipped in the terminal device  150  have the functions similar to those of the communication processing unit  11 , the security countermeasure level data acquisition unit  12  and the control unit  13  shown in  FIG. 1 .  
      The switch  160  is a network device that relays data received from the terminal device  150 , and sends data to a port to which a terminal device or a server device at destination is connected via the network  180 .  
      The switch  160  not only relays data, but also, when it receives the security countermeasure level data from the terminal device  150 , it transfers the received security countermeasure level data to the control server device  170 . The control server device  170  judges an IP address at communication destination that allows the terminal device  150  to communicate, on the basis of the sent security countermeasure level data.  
      The switch  160  receives the judgment result that is sent by the control server device  170 , and memorizes the IP address information in correspondence with the port to which the terminal device  150  is connected. When the data is sent by the terminal device  150 , on the basis of the memorized IP address information, the switch  160  carries out a process to connect the terminal device  150  to the network  180  or a process to reject the connection.  
      The switch  160  includes a communication processing unit  161 , a port control table  162 , a connection control unit  163 , and a control unit  164 . The communication processing unit  161  is a communication processing unit that has the functions similar to those of the communication processing unit  21  shown in  FIG. 1 .  
      The port control table  162  is a table wherein information about the IP addresses set to the respective communication ports of the switch  160  is registered.  FIG. 16  is an example of the port control table  162  shown in  FIG. 15 .  
      As shown in  FIG. 16 , in this port control table  162 , respective information pieces of port number, port status, and identification information are registered. The port number is an identification number that identifies the respective ports that the switch has. The port status is IP address information of the connection destination set to ports to which respective terminal devices are connected. The identification information is information that identifies the port that has received the security countermeasure level data from the terminal device. The identification information is generated at the moment when the security countermeasure level data is accepted from the terminal device, and is sent together with the security countermeasure level data to the control server device  170 .  
      Back to the explanation of  FIG. 15 , the connection control unit  163  is a control unit that refers to the port control table  162 , when it receives data from the terminal device  150  to a terminal device or a server device connected to the network  180 , and thereby limits the connection to the network  180 .  
      Concretely, the connection control unit  163  checks the port status corresponding to the port that has received data, in the port control table  162 , and when the IP address of the destination is included in the IP addresses registered in the port status, it connects to the network  180  and sends the data to the destination. When the port status corresponding to the port that has received the data is the IP address of the update server device  190 , the connection control unit sets the port so that communications should be made only with the update server device  190 .  
      The connection control unit  163  sends the security countermeasure level transfer data wherein identification information is added to the security countermeasure level data, to the control server device  170 , and when it receives judgment result data showing the identification information and IP address judgment result from the control server device  170  in response thereto, the connection control unit carries out a process to set the IP address to the port status of the port corresponding to the identification information concerned in the port control table  162 .  
      The control unit  164  is a control unit that entirely controls the switch  160 , and sends and receives data with the respective functional units.  
      The control server device  170  is a server device that receives the security countermeasure level transfer data from the switch  160 , and judges a terminal device or a server device connected to the network  180  that permits the connection of the terminal device  150  to the network  40 , on the basis of the security countermeasure level data included in the security countermeasure level transfer data.  
      The control server device  170  includes a communication processing unit  171 , connection condition data  172 , a destination IP address judgment unit  173 , and a control unit  174 . The communication processing unit  171  is a communication processing unit that communicates with the switch  160 , and receives the security countermeasure level transfer data that is sent from the switch  160 , and sends out judgment result data to the switch  160 .  
      The connection condition data  172  is data that is referred to at the moment of judgment of a terminal device or a server device to communicate with the terminal device  150 , and memorizes the conditions to decide an IP address at connection destination.  
       FIG. 17  is an example of the connection condition data  172  shown in  FIG. 15 . As shown in  FIG. 17 , in this connection condition data  172 , respective information pieces of security countermeasure level, judgment conditions, condition dissatisfaction filter information, and condition satisfaction filter information are registered.  
      The security countermeasure level includes respective items selected to judge the conditions of computer virus countermeasures, which correspond, to the respective items included in the security countermeasure level data that is sent by the terminal device. The judgment conditions are conditions that the respective items registered in the security countermeasure level should satisfy.  
      The condition dissatisfaction filter information is information about the IP address of the update server device  190  that is to be connected when the respective items included in the security countermeasure level data are not satisfied. The condition satisfaction filter information is information about the IP address of the terminal device or server device that is to be connected when the respective items included in the security countermeasure level data are satisfied. Herein, the condition satisfaction filter information is the IP addresses of all the terminal devices or server devices connected to the network  180 .  
      Back to the explanation of  FIG. 15 , the destination IP address judgment unit  173  judges whether the respective items of the security countermeasure level data included in the security countermeasure level transfer data that the communication processing unit  171  has received satisfy the respective judgment conditions memorized in the connection condition data  172  or not, and sends the judgment result thereof via the communication processing unit  171  to the switch  160 .  
      The control unit  174  is a control unit that entirely controls the control server device  170 , and sends and receives data with the respective functional units.  
      By the way, in the third embodiment, filtering is carried out by use of IP address and the like, while in place of this, as mentioned in the second embodiment, by combination of filtering and limitation of connectable VLAN, safety against virus infection may be further increased.  
      As mentioned above, in the third embodiment, the communication processing unit  161  of the switch  160  accepts the IP address limitation information of the terminal device  150 , judged by the control server device  170  on the basis of the security countermeasure level data of the terminal device  150 , and on the basis of the accepted information, the communication processing unit limits terminal devices or server devices at communication destination with which the terminal device  150  communicates, accordingly, the third embodiment makes it possible to appropriately prevent a computer virus from infecting from the terminal device  150  whose security countermeasures are insufficient to other terminal devices or server devices connected to the network  180 .  
      By the way, in the second embodiment, when the security countermeasure level data is sent by the terminal device, the connection destination of the terminal device is allotted to the update VLAN, while in place of this, when the network cable of the terminal device is connected to the port of the switch, the switch may connect the terminal device first to a confirmation update VLAN wherein the security countermeasure level of the terminal device can be confirmed and updated.  
      Thereby, even if the terminal device is infected by a computer virus, the system makes it possible to prevent the infection from spreading over other devices connected to the network. Further, the system makes it possible to prevent the terminal device from being infected by a computer virus from other devices during the terminal device is updating an OS or an anti virus software program. Therefore, in a fourth embodiment, a case wherein when the network cable of the terminal device is connected to the port of the switch, the switch first connects the terminal device to a confirmation update VLAN is explained hereinafter.  
      In the first place, the structure of a network connection control system according to the fourth embodiment is explained hereinafter.  FIG. 18  is a functional block diagram of a network connection control system according to the fourth embodiment. By the way, detailed explanations about the functional units similar to the functional units in the second embodiment shown in  FIG. 9  are omitted hereinafter.  
      As shown in  FIG. 18 , in this network connection control system, a terminal device  200  and a switch  210  are connected with each other, and the switch  210  and a control server device  220  and an update server device  250  are connected via a confirmation update VLAN  240 , and the switch  210  is connected to a VLAN  230 .  
      The confirmation update VLAN  240  is a VLAN wherein the control server device  220 , and the update server device  250  that enables the terminal device  200  to update an OS or an anti virus software program are connected, while the VLAN  230  is a VALN that is used when the terminal device  200  carries out communications with other terminal devices or server devices (not shown).  
      The terminal device  200  is a terminal device such as a personal computer to which various application software programs are installed, and a communication processing unit  201 , a security countermeasure level data acquisition unit  202  and a control unit  203  equipped in the terminal device  200  have the functions similar to those of the communication processing unit  81 , the security countermeasure level data acquisition unit  82  and the control unit  83  shown in  FIG. 9 .  
      The switch  210  is a network device that relays data received from the terminal device  200 , and sends data to a port to which a terminal device or a server device at destination is connected via the VLAN  230 .  
      The switch  210  not only relays data, but also, when the terminal device  200  is connected to the switch  210 , it carries out a process to connect the confirmation update VLAN  240  that enables to confirm and update the security countermeasure level of the terminal device  200 .  
      When this switch  210  receives the security countermeasure level data from the terminal device  200 , it transfers the received security countermeasure level data to the control server device  220 . The control server device  220  judges the VLAN to which the terminal device  200  should be connected, on the basis of the sent security countermeasure level data.  
      Then, the switch  210  receives the judgment result that is sent by the control server device  220 , and memorizes the VLAN information in correspondence with the port to which the terminal device  200  is connected. When the data is sent by the terminal device  200 , on the basis of the memorized VLAN address information, the switch  210  carries out a process whether to keep the terminal device  200  connected to the confirmation update VLAN  240 , or to switch the terminal device to the VLAN  230  as the connection destination thereof.  
      The switch  210  includes a communication processing unit  211 , a port control table  212 , a connection control unit  213 , and a control unit  214 . The communication processing unit  211  is a communication processing unit that communicates with the terminal device  200  and the control server device  220 . A process to relay communications among the terminal device  200  and terminal devices or server devices (not shown) connected to the VLAN  230  is carried out.  
      Concretely, when the network cable of the terminal device  200  is connected to the port of the switch  210 , this communication processing unit  211  connects the terminal device  200  to the confirmation update VLAN  240 .  
      The communication processing unit accepts the data that is sent by the terminal device  200 , and when the accepted data is the security countermeasure level data, the communication processing unit adds the information of the port that has accepted the data to the security countermeasure level data, and transfers the data to the control server device  220 . When the data accepted from the terminal device  200  is other data than the security countermeasure level data, the communication processing unit transfers the data to the connection control unit  213 .  
      The port control table  212  is a table similar to the port control table  92  shown in  FIG. 10 .  
      The connection control unit  213  is a control unit that refers to the port control table  212  when it receives data from the terminal device  200  to a terminal device or a server device connected to the VLAN  230 , and thereby judges the connection propriety to the VLAN  230 .  
      Concretely, the connection control unit  213  permits the connection to the VLAN  230  when the port status corresponding to the port that has received data is set to the VLAN  230  in the port control table  212 , and sends the data to the port corresponding to the VLAN  230 . While it rejects the connection to the VLAN  230 , and set the port so that communications should be made only with the update VLAN  240  when the port status corresponding to the port that has received the data is set to the update VLAN  240 .  
      The connection control unit  213  sends the security countermeasure level transfer data wherein identification information is added to the security countermeasure level data, to the control server device  220 , and when it receives the identification information from the control server device  220  and judgment result data showing the judgment result of the VLAN to which the terminal device  200  is to be connected, in response thereto, it carries out a process to set the port status of the port corresponding to the identification information concerned in the port control table  212 .  
      The control server device  220  is a server unit that receives the security countermeasure level transfer data from the switch  210 , and judges which VLAN the terminal device  200  should be connected to, on the basis of the security countermeasure level data included in the security countermeasure level transfer data.  
      A communication processing unit  221 , connection condition data  222 , a connection destination VLAN judgment unit  223  and a control unit  224  equipped in the control server device  220  have the functions similar to those of the communication processing unit  101 , the connection condition data  102 , the connection destination VLAN judgment unit  103  and the control unit  104  shown in  FIG. 9 .  
      However, in the condition dissatisfaction VLAN switching destination information of the connection condition data  222 , the information of the confirmation update VLAN  240  is registered, therefore, only when the respective conditions of the connection condition data  222  are satisfied, the connection is made to other VLAN registered in the condition satisfaction VLAN switching destination information, namely, the VLAN  230 .  
      As mentioned above, in the fourth embodiment, when the terminal device  200  is connected to the switch  210 , the communication processing unit  211  of the switch  210  connects the terminal device  200  to the confirmation update VLAN  240  that can confirm and update the security countermeasure level of the terminal device  200 , accordingly, the fourth embodiment makes it possible to appropriately prevent a computer virus from infecting from the terminal device  200  whose security countermeasures are insufficient to other terminal devices or server devices connected to the VLAN  230 .  
      By the way, in the first embodiment through the fourth embodiment, when the security countermeasure level of the terminal device is checked, authentication process to a user is not performed, while, security may be further improved by use of user authentication. Therefore, in a fifth embodiment, a case wherein user authentication is performed when the security countermeasure level of the terminal device is confirmed is explained hereinafter.  
      In the first place, the structure of a network connection control system according to the fifth embodiment is explained hereinafter.  FIG. 19  is a functional block diagram of a network connection control system according to the fifth embodiment. By the way, detailed explanations about the similar functional units to the functional units in the first embodiment shown in  FIG. 1  are omitted hereinafter.  
      As shown in  FIG. 19 , in this network connection control system, a terminal device  260  and a switch  270  are connected with each other, and the switch  270  and a control server device  280  are connected with each other, and an authentication server device  280  and a control server device  290  are connected with each other, and the switch  270  is connected to a network  300  to which plural terminal devices and server devices (not shown) are connected.  
      The terminal device  260  is a terminal device such as a personal computer to which various application software programs are installed. The terminal device  260  includes a communication processing unit  261 , a security countermeasure level data acquisition unit  262  and a control unit  263 .  
      The communication processing unit  261  is a communication processing unit that carries out communications with other connected terminal devices, server devices, the switch  270  and the like via the network. The security countermeasure level data acquisition unit  262  is an acquisition unit that acquires the computer virus countermeasure conditions of the terminal device  260  as security countermeasure level data. The acquired security countermeasure level data is sent by the communication processing unit  261  to the switch  270 . At this moment, the communication processing unit  261  sends the security countermeasure level data including user authentication information to the switch  270 .  
       FIG. 20  is an example of security countermeasure level data  310  that the terminal device  260  sends. As shown in  FIG. 20 , this security countermeasure level data  310  includes information pieces of OS (Operating System) type, OS update time and date, anti virus software program version, anti virus software engine version, and anti virus software pattern version.  
      Back to the explanation of  FIG. 19 , the control unit  263  is a control unit that entirely controls the terminal device  260 , and sends and receives data with the respective functional units.  
      The switch  270  is a network device that relays the data received from the terminal device  260 , and sends the data to a port to which a terminal device or a server device at destination is connected via a network.  
      The switch  270  not only relays data, but also, when it receives the security countermeasure level data  310  from the terminal device  260 , it carries out a process to transfer the security countermeasure level data  310  to the authentication server device  280 .  
      The authentication server device  280  carries out user authentication, and only when the authentication is successful, it transfers the security countermeasure level data  310  to the control server device  290 , and the control server device  290  judges connection propriety of the terminal device  260  to the network  300 , on the basis of the security countermeasure level data  310 . When the authentication fails, the authentication server device  280  sends authentication failure information to the switch  270 .  
      When the switch  270  receives the data showing the connection propriety to the network  300  judged by the control server device  290 , it memorizes the data in correspondence to the port to which the terminal device  260  is connected. When the data is sent by the terminal device  260 , the switch carries out a process to connect the terminal device  260  to the network  300  or reject the connection, on the basis of the memorized connection propriety information. When the switch accepts authentication failure information by the authentication server device  280 , it memorizes “connection rejection” information in correspondence to the port to which the terminal device  260  is connected.  
      The switch  270  includes a communication processing unit  271 , a port control table  272 , a connection control unit  273 , and a control unit  274 . The communication processing unit  271  is a communication processing unit that communicates with the terminal device  260  and the authentication server device  280 . The communication processing unit also carries out a process to relay communications with a terminal device or a server device connected to the terminal device  260  and the network  300 .  
      Concretely, when the data accepted from the terminal device  260  is the security countermeasure level data  310 , this communication processing unit  271  generates security countermeasure level transfer data wherein the information of the port that has accepted the data is added to the security countermeasure level data  310 , and transfers that data to the authentication server device  280 . While, when the data accepted from the terminal device  260  is other data than the security countermeasure level data  310 , the communication processing unit transfers that data to the connection control unit  273 .  
       FIG. 21  is an example of security countermeasure level transfer data  320  that the switch  270  sends. As shown in  FIG. 21 , this security countermeasure level transfer data  320  includes information pieces of identification information, user ID, encoded password, OS (Operating System) type, OS update time and date, anti virus software program version, anti virus software engine version, and anti virus software pattern version.  
      The identification information is an identification number that identifies the port at which the switch  270  accepts the data from the terminal device  260 , while the user ID, the encoded password, the OS (Operating System) type, the OS update time and date, the anti virus software program version, the anti virus software engine version, and the anti virus software pattern version are the respective information pieces included in the security countermeasure level data  310 .  
      Back to the explanation of  FIG. 19 , the port control table  272  is a table wherein the information about the communication permission or rejection set to each communication port of the switch  270  is registered, and is a table similar to the port control table  22  shown in  FIG. 4 .  
      The connection control unit  273  is a control unit that refers to the port control table  272  when it receives data from the terminal device  260  to a terminal device or a server device connected to the network  300 , and thereby controls the connection of the terminal device  260  to the network  300 .  
      Concretely, the connection control unit  273  rejects data communications when the port status corresponding to the port that has received the data is set to “connection rejection” in the port control table  272 , while it permits data communications, and carries out a process to send data to the port to which the terminal device or the server device at communication destination is connected when the port status is set to “connection permission”.  
      The connection control unit  273  sends the security countermeasure level transfer data  320  wherein identification information is added to the security countermeasure level data  310 , to the authentication server device  280 , and when it receives authentication judgment result data from the authentication control server device  280  in response thereto, it carries out a process to set the port status in the port control table  272 .  
      Concretely, when the authentication result information included in the authentication judgment result data is “authentication success”, the connection control unit sets the port status of the port control table  272  on the basis of the connection propriety judgment result judged by the control server device  290  included in the authentication judgment result data. When the authentication result information is “authentication failure”, the connection control unit sets the port status of the port control table  272  to “connection rejection”.  
      The control unit  274  is a control unit that entirely controls the switch  270 , and sends and receives data with the respective functional units.  
      The authentication server device  280  is a server device such as an RADIUS (Remote Authentication Dial-In User Services) server that accepts the security countermeasure level transfer data  320  including user authentication information from the switch  270 , and thereby carries out user authentication. The authentication server device  280 , when user authentication succeeds, transfers the security countermeasure level data wherein user authentication information is deleted from the security countermeasure level transfer data  320 , to the control server device  290 .  
      The authentication server  280  includes a communication processing unit  281 , user authentication data  282 , an authentication process unit  283 , and a control unit  284 . The communication processing unit  281  is a processing unit that performs communications with the switch  270  and the control server device  290 .  
      Concretely, this communication processing unit  281  accepts the security countermeasure level transfer data  320  from the switch  270 , and acquires the authentication information included in the security countermeasure level transfer data  320 , and informs the authentication process unit  283  of the authentication information. When the user authentication by the authentication process unit  283  succeeds, this communication processing unit  281  sends to the control server device  290  the security countermeasure data wherein the user authentication information is deleted from the security countermeasure level transfer data  320 .  
      Then, when this communication processing unit  281  accepts, on the basis of the security countermeasure level data sent to the control server device  290 , the judgment result information wherein the connection propriety of the terminal device  260  to the network  300  is judged by the control server device  290 , together with the port identification information, the communication processing unit sends authentication judgment result data wherein further authentication success information is added to the above information pieces to the switch  270 .  
      When the user authentication fails, the communication processing unit  281  sends authentication judgment result data including the port identification information and the authentication failure information to the switch  270 .  
      The user authentication data  282  is data wherein user authentication information is registered, and is referred to when the authentication process unit  283  carries out user authentication. The authentication process unit  283  accepts the authentication information included in the security countermeasure level transfer data  320  by the communication processing unit  281 , and when the authentication information is same as the authentication information registered in the user authentication data  282 , the authentication process unit judges that the user authentication has succeeded, and instructs the communication processing unit  281  to send the security countermeasure level data to the control server device  290 .  
      The control server device  290  is a device that receives the security countermeasure level data from the authentication server device  280 , and judges whether or not to permit the connection of the terminal device  260  to the network  300 , on the basis of the security countermeasure level.  
      The control server device  290  includes a communication processing unit  291 , communication condition data  292 , a connection propriety judgment unit  293  and a control unit  294 . The communication processing unit  291  is a communication processing unit that communicates with the authentication server device  280 , and receives the security countermeasure level data sent from the authentication server device  280 , and sends out judgment result data wherein whether or not to permit the connection of the terminal device  260  to the network  300  is judged to the authentication server device  280 .  
      The communication condition data  292  is data that is referred to when whether or not to connect the terminal device  260  to the network  300  is judged, and conditions to decide connection propriety is memorized therein. Concretely, the communication condition data is data similar to the connection condition data  32  shown in  FIG. 6 .  
      The connection propriety judgment unit  293  judges whether the respective items of the security countermeasure level data that the communication processing unit  291  has received satisfy the respective judgment conditions memorized in the connection condition data  292  or not, and generates the judgment result data similar to the judgment result data  70  shown in  FIG. 5 , and carries out a process to send the judgment result data via the communication processing unit  291  to the authentication server device  280 .  
      The control unit  294  is a control unit that entirely controls the control server device  290 , and sends and receives data with the respective functional units.  
      The process procedure of the connection control process that the switch  270  according to the fifth embodiment performs are explained hereinafter.  FIG. 22A  and  FIG. 22B  are flow charts ( 1 ) and ( 2 ) respectively showing the process procedure of the connection control process that the switch  270  according to the fifth embodiment conducts.  
      As shown in  FIG. 22A , first, the communication processing unit  271  of the switch  270  receives data (step S 501 ). The communication processing unit  271  judges whether the data has be received at the port at the side of the terminal device  260  or not (step S 502 ), and when the data has been received at the port at the side of the terminal device  260  (step S 502 , Yes), the communication processing unit checks whether the received data is the security countermeasure level data  310  or not (step S 503 ).  
      When the received data is not the security countermeasure level data  310  (step S 503 , No), the connection control unit  273  refers to the port control table  272  and confirms the port status corresponding to the port that has received the data (step S 504 ), and checks whether the port status is “connection rejection” or not (step S 505 ).  
      When the port status is not “connection rejection” (step S 505 , No), the connection control unit  273  sends the received data via the network  300  to a terminal device or a server device at destination (step S 506 ), and completes the connection control process. When the port status is “connection rejection” (step S 505 , Yes), the connection control unit  273  deletes the data received from the terminal device  260  (step S 510 ), and completes the connection control process.  
      In the step S 503 , when the data received from the terminal device  260  is the security countermeasure level data  310  (step S 503 , Yes), the communication processing unit  271  generates identification information that identifies the port that has received the data (step S 507 ), and transfers the security countermeasure level transfer data  320  wherein the identification information is added to the security countermeasure level data  310  to the authentication server device  280  (step S 508 ).  
      Then, the communication processing unit  271  stores the identification information into the port control table  272  in correspondence to the port that has received the data (step S 509 ), and completes the connection control process.  
      In the step S 502 , when the data has not been received at the port at the side of the terminal device  260 , but received at the port at the side of the authentication server device  280  (step S 502 , No), as shown in  FIG. 22B , the communication processing unit  271  checks whether the received data is the judgment result data sent in response to the security countermeasure level transfer data  320  sent to the authentication server device  280  or not (step S 511 ).  
      When the received data is the judgment result data (step S 511 , Yes), the connection control unit  273  searches for a port having the identification information that corresponds to the identification information included in the judgment result data from the port control table  272  (step S 512 ), and checks whether there is a port whose identification information corresponds to the identification information included in the judgment result data or not (step S 513 ).  
      When there is a port whose identification information corresponds to the identification information included in the judgment result data (step S 513 , Yes), the connection control unit  273  checks whether the authentication has succeeded or not from the authentication judgment result (step S 514 ), and when the authentication has succeeded (step S 514 , Yes), the connection control unit sets the port status “connection permission” or “connection rejection” in correspondence to the port whose identification information corresponds, according to the judgment result included in the authentication judgment result data (step S 515 ), and clears the identification information of the port control table  272  (step S 516 ), and completes the connection control process.  
      When the authentication fails (step S 514 , No), the connection control unit  273  sets the port status of “connection rejection” in correspondence to the port whose identification information corresponds (step S 519 ), and clears the identification information of the port control table  272  (step S 516 ), and completes the connection control process.  
      In the step S 513 , when there is not any port whose identification information corresponds (step S 513 , No), the connection control unit  273  deletes the authentication judgment result data (step S 517 ), and completes the connection control process.  
      In the step S 511 , when the received data is not the authentication judgment result data (step S 511 , No), the connection control portion  273  confirms the port status of the port corresponding to the destination of the data concerned in the port control table  272  (step S 518 ), and as shown in  FIG. 22A , the connection control portion checks whether the port status is “connection rejection” or not (step S 505 ).  
      When the port status is not “connection rejection” (step S 505 , No), the connection control unit  273  sends the data received from the authentication server device  280  to a terminal device or a server device at destination (step S 506 ), and completes the connection control process. When the port status is “connection rejection” (step S 505 , Yes), the connection control unit  273  deletes the data received from the authentication server device  280  (step S 510 ), and completes the connection control process.  
      The process procedure for the user authentication process that the authentication server device  280  according to the fifth embodiment performs is explained hereinafter.  FIG. 23  is a flow chart of the process procedure of the user authentication process that the authentication server device  280  according to the fifth embodiment performs.  
      As shown in  FIG. 23 , first, the communication processing unit  281  of the authentication server device  280  receives the security countermeasure level transfer data  320  to which the port identification information has been added (step S 601 ). The authentication process unit  283  compares the authentication information included in the security countermeasure level transfer data  320 , and the authentication information registered in the user authentication data  282 , and performs the user authentication process (step S 602 ).  
      Then, the authentication process unit  283  check whether the user authentication has succeeded or not (step S 603 ), and when the user authentication has succeeded (step S 603 , Yes), the authentication process unit sends the security countermeasure level data to which the identification information has been added, to the control server device  290  (step S 604 ).  
      The authentication process unit  283  receives the judgment result data from the control server device  290  (step S 605 ), and checks whether the judgment result of connection propriety included in the judgment result data is “connection rejection” or not (step S 606 ).  
      When the judgment result is not “connection rejection” (step S 606 , No), the authentication process unit  283  adds the authentication judgment result of authentication success to the judgment result data received from the control server device  290  and thereby generates authentication judgment result data (step S 607 ), and sends the authentication judgment result data via the communication processing unit  281  to the switch  270  (step S 608 ).  
      When the judgment result is “connection rejection” (step S 606 , Yes), the authentication process unit  283  adds the authentication judgment result of authentication failure to the judgment result data received from the control server device  290  and thereby generates authentication judgment result data (step S 609 ), and sends the authentication judgment result data via the communication processing unit  281  to the switch  270  (step S 608 ).  
      In the step S 603 , when the user authentication has not succeeded (step S 603 , No), the authentication process unit  283  adds the authentication judgment result of authentication failure to the identification information and thereby generates authentication judgment result data (step S 609 ), and sends the authentication judgment result data via the communication processing unit  281  to the switch  270  (step S 608 ).  
      By the way, in the fifth embodiment, the connection authentication of the terminal device  260  that is connected to the network  300  is performed, while in place of this, as shown in the second embodiment, the connection authentication of the terminal device that is connected to VLAN may be performed.  
      As mentioned above, in the fifth embodiment, when the connection authentication of the terminal device  260  by the authentication process unit  283  of the authentication server device  280  fails, the communication processing unit  271  of the switch  270  receives the connection rejection information of the terminal device  260  to the network  300  generated by the authentication process unit  283  of the authentication server device  280 , and the connection control unit  273  of the switch  270  rejects the connection of the terminal device  260  to the network  300 , on the basis of the connection rejection information, accordingly, by further performing the connection authentication, the fifth embodiment makes it possible to appropriately prevent a computer virus from infecting from a computer whose security countermeasures are insufficient to other computers connected to the network.  
      By the way, in the first embodiment through the fifth embodiment, when the terminal device sends the security countermeasure level data, the port control table of the switch to set the connection control to the network is updated, while in place of this, the terminal device may connect to the update server device and update the software, and when the security countermeasure level is updated, the terminal device may send the security countermeasure level data again, thereby the port control table of the switch may be updated efficiently.  
      Therefore, in a sixth embodiment, a case wherein when the security countermeasure level has been updated, the terminal device sends the security countermeasure level data again, thereby the port control table of the switch is updated efficiently is explained hereinafter.  
       FIG. 24  is a functional block diagram of a network connection control system according to the sixth embodiment. By the way, detailed explanations about the similar functional units to the functional units in the second embodiment shown in  FIG. 9  are omitted hereinafter.  
      As shown in  FIG. 24 , in this network connection control system, a terminal device  330  and a switch  340  are connected with each other, and the switch  340  and a control server device  350  are connected with each other, and a VLAN  360 , and an update VLAN  370  to which an update server device  380  is connected are connected to the switch  340 .  
      The update VLAN  370  is a VLAN wherein the terminal device  330  is connected to an update server device  380  that can update an OS or an anti virus software program, while the VLAN  360  is a VLAN that is used when the terminal device  360  carries out communications with other terminal device or server device (not shown).  
      The terminal device  330  is a terminal device such as a personal computer to which various application software programs are installed. The terminal device  330  includes a communication processing unit  331 , a security countermeasure level data acquisition unit  332 , a security countermeasure level update detection unit  333 , and a control unit  334 .  
      The communication processing unit  331  is a communication processing unit that carries out communications with the switch  340 , and other terminal devices and server devices connected via the VLAN  360  or the update VLAN  370 . The security countermeasure level data acquisition unit  332  is an acquisition unit that acquires the computer virus countermeasure conditions of the terminal device  330  as security countermeasure level data. The acquired security countermeasure level data is sent by the communication processing unit  331  to the switch  340 .  
      The security countermeasure level update detection unit  333  detects that the terminal device  330  is connected to the update VLAN  370 , and the software is updated by communications with the update server device  380 , and instructs the security countermeasure level data acquisition unit  332  to acquire the security countermeasure level data again, and, the acquired security countermeasure level data is sent again by the communication processing unit  331  to the switch  340 .  
      The control unit  334  is a control unit that entirely controls the terminal device  330 , and sends and receives data with the respective functional units.  
      The respective functional units of the switch  340  and the control server device  350  have functions similar to those of the respective functional units of the switch  90  and the control server device  100  shown in  FIG. 9 .  
      Namely, the switch  340  relays the data received from the terminal device  330 , and controls connection to the VLAN  360  or the update VLAN  370  to which the terminal device or the server device at communication destination is connected.  
      The switch  340  not only relays data, but also, when it receives the security countermeasure level data from the terminal device  330 , it transfers the received security countermeasure level data to the control server device  350 . The control server device  350  judges the VLAN to which the terminal device  330  should be connected, on the basis of the sent security countermeasure level data.  
      Then, the switch  340  receives the judgment result that is sent by the control server device  350 , and memorizes the VALN information into the port control table  342  in correspondence with the port to which the terminal device  330  is connected. When the data is sent by the terminal device  330 , on the basis of the memorized VLAN information, the switch carries out a process to connect the terminal device  330  to the VLAN  360  or the update VLAN  370  or a process to reject the connection.  
      The control server device  350  receives the security countermeasure level data from the switch  340 , and judges the VLAN to which the terminal device  330  should be connected, on the basis of the security countermeasure level data.  
      By the way, in the sixth embodiment, the functional unit to detect the update of the security countermeasure level is added to the terminal device in the second embodiment, while in place of this, the same functional unit may be added to the terminal device in the third embodiment through the fifth embodiment, thereby the process to detect that the software has been updated may be performed.  
      As mentioned above, in the sixth embodiment, when the security countermeasure level update detection unit  333  of the terminal device  330  detects that the terminal device  330  is connected to the update VLAN  370 , and the software is updated, the communication processing unit  341  of the switch  340  accepts the information of the VLAN  360  or the update VLAN  370  to which the terminal device  330  is connected, judged by the control server device  350  on the basis of the updated security countermeasure level data of the terminal device  330 , and the connection control unit  343  of the switch  340  limits the VALN that the terminal device  330  permits to connect to the VLAN  360  or the update VLAN  370  on the basis of the accepted data, accordingly, when the security countermeasure level of the terminal device  330  is updated, the update concerned may be reflected efficiently to the connection restriction of the terminal device  330 .  
      By the way, in the sixth embodiment, when the security countermeasure level of the terminal device is updated, the terminal device sends again the security countermeasure level data, and the port control table of the switch is updated, while in place of this, when the connection condition data of the control server device wherein the security countermeasure level conditions that the terminal device should satisfy are registered is updated, a request may be made for the terminal device to send the security countermeasure level data, and thereby the conditions of the connection control of the terminal device to the network may be changed promptly on the basis of the updated connection condition data.  
      Therefore, in a seventh embodiment, a case wherein when the connection condition data of the control server device is updated, a request is made for the terminal device to send the security countermeasure level data, and thereby the conditions of the connection control of the terminal device to the network are changed on the basis of the security countermeasure level data and the updated connection condition data is explained hereinafter.  
       FIG. 25  is a functional block diagram of a network connection control system according to the seventh embodiment. By the way, detailed explanations about the similar functional units to the functional units in the second embodiment shown in  FIG. 9  are omitted hereinafter.  
      As shown in  FIG. 25 , in this network connection control system, a terminal device  390  and a switch  400  are connected with each other, and the switch  400  and a control server device  410  are connected with each other, and a VLAN  420 , and an update VLAN  430  to which an update server device  440  is connected are connected to the switch  400 .  
      The update VLAN  430  is a VLAN wherein the terminal device  390  is connected to the update server device  440  that can update an OS or an anti virus software program, while the VLAN  420  is a VLAN that is used when the terminal device  390  carries out communications with other terminal device or server device (not shown).  
      The terminal device  390  is a terminal device such as a personal computer to which various application software programs are installed. The terminal device  390  includes a communication processing unit  391 , a security countermeasure level data acquisition unit  392 , and a control unit  393 .  
      The communication processing unit  391  is a communication processing unit that carries out communications with the switch  400 , and other terminal devices and server devices connected via the VLAN  360  or the update VLAN  370 . The communication processing unit  391 , when it receives the security countermeasure level send request that is sent by the control server device  410 , instructs the security countermeasure level data acquisition unit  392  to acquire the security countermeasure level data, and sends the acquired security countermeasure level data to the switch  400 .  
      The security countermeasure level data acquisition unit  392  is an acquisition unit that acquires the computer virus countermeasure conditions of the terminal device  390  as security countermeasure level data. The acquired security countermeasure level data is sent by the communication processing unit  391  to the switch  400 .  
      The control unit  393  is a control unit that entirely controls the terminal device  390 , and sends and receives data with the respective functional units.  
      The respective functional units of the switch  400  have functions similar to those of the respective functional units of the switch  90  shown in  FIG. 9 . Namely, the switch  400  relays the data received from the terminal device  390 , and controls connection to the VLAN  420  or the update VLAN  430  to which the terminal device or server device at communication destination is connected.  
      The switch  400  not only relays data, but also, when it receives the security countermeasure level data from the terminal device  390 , it transfers the received security countermeasure level data to the control server device  410 . The control server device  410  judges the VLAN to which the terminal device  390  should be connected, on the basis of the sent security countermeasure level data.  
      Then, the switch  400  receives the judgment result sent by the control server device  410 , and memorizes the VALN information into the port control table  402  in correspondence with the port to which the terminal device  390  is connected. When the data is sent by the terminal device  390 , on the basis of the memorized VLAN information, the switch carries out a process to connect the terminal device  390  to the VLAN  420  or the update VLAN  430  or a process to reject the connection.  
      The control server device  410  is a server device that receives the security countermeasure level data from the switch  400 , and judges the VLAN to which the terminal device  390  should be connected, on the basis of the security countermeasure level data.  
      The control server device  410  includes a communication processing unit  411 , connection condition data  412 , a connection condition update detection unit  413 , a connection destination VLAN judgment unit  414 , and a control unit  415 . The communication processing unit  411  is a communication processing unit that performs communications with the switch  400 , and receives the security countermeasure level transfer data sent from the switch  400 , and sends out judgment result data of the VLAN to which the terminal device  390  should be connected to the switch  400 .  
      The connection condition data  412  is data similar to the connection condition data  102  shown in  FIG. 12 , and is referred to at the moment to judge the VLAN to which the terminal device  390  should be connected, and memorizes the conditions to decide the connection destination VLAN.  
      The connection condition update detection unit  413  detects changes in the security countermeasure level item kinds, judgment conditions, condition satisfaction VLAN switching destination information or condition dissatisfaction VLAN switching destination information registered in the connection condition data  412 , and sends request data that requests the terminal device  390  to send the security countermeasure level data again.  
      The connection destination VLAN judgment unit  414  judges whether the respective items of the security countermeasure level data that the communication processing unit  411  has received satisfy the respective judgment conditions memorized in the connection condition data  412  or not, and sends the judgment result of the VLAN to which the terminal device  80  should be connected, via the communication processing unit  411  to the switch  400 .  
      The control unit  415  is a control unit that entirely controls the terminal device  410 , and sends and receives data with the respective functional units.  
      By the way, in the seventh embodiment, the functional unit to detect the update of the connection condition data is added to the control server device in the second embodiment, while in place of this, the same functional unit may be added to the terminal device in the third embodiment through the sixth embodiment, thereby the process to detect the update of the connection condition data may be performed.  
      In the seventh embodiment, when the connection condition data  412  of the control server device  410  is updated, the control server device  410  requests the terminal device  330  to send the security countermeasure level data again, while in place of this, as shown in the sixth embodiment, when the terminal device  330  has already sent the security countermeasure level data, the VLAN that the terminal device  330  permits to connect may be set without making a send request.  
      As mentioned above, in the seventh embodiment, when the connection condition update detection unit  413  of the control server device  410  detects that the connection condition data  412  of the control server device  410  has been updated, the communication processing unit  341  of the switch  340  accepts the information of the VLAN  360  or the update VLAN  370  to which the terminal device  330  should be connected, on the basis of the security countermeasure level data resent from the terminal device  330 , and the connection control unit  343  of the switch  340  limits the VALN that the terminal device  330  permits to connect to the VLAN  360  or the update VLAN  370 , accordingly, when the connection condition data  412  of the control server device  410  is updated, the update may be reflected efficiently to the connection restriction of the terminal device  330 .  
      The embodiments according to the present invention have been explained heretofore, while the concrete structural forms thereof are not limited to those embodiment explained above, but the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.  
      For example, in the first embodiment through the seventh embodiment, a program that realizes the functions of the terminal device, the switch, the control server device and the authentication server device may be recorded into a recording medium from which the program may be read by a computer, and the program recorded in this recording medium may be read and run by the computer to realize the respective functions.  
       FIG. 26  is a block diagram showing the structure of a computer  500  in a modified example of the embodiment. The computer  500  shown in  FIG. 26  includes a CPU (Central Process Unit)  510  that runs the above program, an input device  520  including a keyboard, a mouse or so, a ROM (Read Only memory)  530  that memorizes various kinds of data, a RAM (Random Access memory)  540  that memorizes calculation parameters and the like, a reader  550  that reads the program from a recording medium  600  that records the program that realizes the functions of the terminal device, the switch, the control server device and the authentication server device, and an output device  560  including a display, a printer and the like.  
      The CPU  510  reads the program recorded in the recording medium  600  via the reader  550 , and then runs the program, thereby realizes the functions mentioned above. By the way, as the recording medium  600 , an optical disk, a flexible disk, a hard disk and the like may be employed. The program may be introduced to the computer  500  via a network including internet and the like.  
      Further, in the first embodiment through the seventh embodiment, the switch and the control server device are arranged separately; however, a switch may be so structured to realize both the functions of the switch and those of the control server device. In the same manner, in the fifth embodiment, the switch, the authentication server device, and the control server device are arranged separately; however, a switch may be so structured to realize both the functions of the switch and those of the authentication server device, furthermore, a switch may be so structured to realize all the functions of the switch, those of the authentication server device, and those of the control server device.  
      According to the present invention, connection control information concerning connection control generated on the basis of security countermeasure condition information concerning computer security countermeasure conditions of a specified computer is accepted, and on the basis of the accepted connection control information, the connection of the specified computer to a network is controlled, accordingly, it is possible to appropriately prevent a computer being infected by a computer virus from another computer whose security countermeasures are insufficient.  
      According to the present invention, the connection of a specified computer to the network is accepted or rejected on the basis of the accepted connection control information, thereby the connection of computers whose security countermeasures are insufficient is rejected, accordingly, a further effect is attained to appropriately prevent a computer virus from infecting to other computers connected to the network.  
      Further, according to the present invention, when a network is divided into plural networks, networks that permit the connection of specified computers in plural networks are limited on the basis of the accepted connection control information, and those networks to which computers whose security countermeasures are insufficient are blocked, and the connection to other networks than specified is rejected, accordingly, a still further effect is attained to appropriately prevent a computer virus from infecting to other computers connected to the network.  
      Still further, according to the present invention, when a specified computer is set enable to communicate via a network, the network which permits the connection of the specified computer is restricted, and a network to which the connection is permitted accepts connection control information generated on the basis of security countermeasure condition information of the restricted specified computer, thereby networks to which computers whose security countermeasures are insufficient are blocked when computers are set enable to communicate via networks, and communications with other computers than designated are rejected, accordingly, another effect is attained to appropriately prevent a computer virus from infecting to other computers connected to the network.  
      Moreover, according to the present invention, computers at communication destinations to communicate with a specified computer are limited on the basis of accepted connection control information, and the connection of the specified computer to network is permitted or rejected, thereby computers at communication destinations whose security countermeasures are insufficient are restricted, and communications with other computers than designated are rejected, accordingly, further another effect is attained to appropriately prevent a computer virus from infecting to other computers connected to the network.  
      According to the present invention, when a specified computer is set enable to communicate via a network, computers at communication destinations to communicate with the specified computer are limited, and computers at communication destinations accepts connection control information generated on the basis of security countermeasure condition information of the restricted specified computer, and computers at communication destinations whose security countermeasures are insufficient to communicate with the specified computer are limited when computers are set enable to communicate via networks, and communications with other computers than designated are rejected, accordingly, still further another effect is attained to appropriately prevent a computer virus from infecting to other computers connected to the network.  
      Still further, according to the present invention, after connection control of a specified computer to network, when the security countermeasure condition information of the specified computer is updated, connection control information concerning connection control generated on the basis of the updated security countermeasure condition information is accepted, and connection control of the specified computer to network is updated on the basis of the accepted connection control information, accordingly, another effect is attained to effectively reflect an update of security countermeasures of computers connected to the network to the connection control of computers to the network.  
      Moreover, according to the present invention, when connection control conditions to specify the connection control of a specified computer to network are updated, connection control information concerning connection control generated on the basis of security countermeasure condition information and connection control conditions is accepted again, and the connection control of the specified computer to network is updated on the basis of the accepted connection control information, accordingly, still another effect is attained to effectively reflect an update of the connection control conditions that specify the connection control of computers, to the connection control of computers to the network.  
      According to the present invention, information concerning connection authentication of a specified computer is further accepted, and the connection control procedures reject the connection of the specified computer to network when information concerning the connection authentication accepted by the connection control information acceptance procedures is information showing authentication failure, and thereby information of connection authentication results of computers is accepted, accordingly, still further another effect is attained to further appropriately prevent a computer virus from infecting from a computer whose security countermeasures are insufficient to other computers connected to the network.  
      Still further, according to the present invention, connection authentication of a specified computer is further performed, and when the connection authentication fails, connection of the specified computer to network is rejected, and connection authentication of the computer is further performed, accordingly, a still another effect is attained to further appropriately prevent a computer virus from infecting from a computer whose security countermeasures are insufficient to other computers connected to the network.  
      Moreover, according to the present invention, security countermeasure condition information concerning computer security countermeasure conditions of a specified computer is accepted, and whether the security countermeasure conditions are sufficient or not is judged, and the connection of the specified computer to network is controlled on the basis of the judged judgment result, accordingly, a still another effect is attained to appropriately prevent a computer virus from infecting from a computer whose security countermeasures are insufficient to other computers connected to the network.  
      According to the present invention, connection authentication of a specified computer is further performed, and when the connection authentication fails, the connection of the specified computer to network is rejected, accordingly, yet a further effect is attained to further appropriately prevent a computer virus from infecting from a computer whose security countermeasures are insufficient to other computers connected to the network.  
      Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.