A security module server device for transmitting, over a network, a dynamic security module to a user terminal and receiving, over the network, notification details of a security management event from the user terminal wherein the security management event includes at least one of (a) details used to determine parameters of the dynamic security module, (b) details of states in which the dynamic security module runs, (c) security management result information indicating that there has been a hacking threat at the user terminal, (d) details concerning treatment of computer viruses for an application program installed on the user terminal, the security module server device comprising: a communication unit configured to transmit, over the network, the dynamic security module and to receive the security management event; and a processor configured to: control the communication unit; create a security session with a security client of the user terminal, wherein the security session is created by generating and storing a session ID and transmitting the session ID to the security client; store a plurality of dynamic security modules having different code structures or algorithms, wherein a first of the plurality of dynamic security modules varies in one or more variable portions thereof from a second of the plurality of dynamic security modules and wherein a part or all of said code structures or algorithms of each of said plurality of dynamic security modules has a predetermined validity period that limits its code's functionality at the user terminal, and each of the least two dynamic security modules is arranged to perform security management in the security client of the user terminal to protect the user terminal from malicious attack or infection of an application program with a virus and, when the validity period expires, the security module is configured to delete part or all of the code or stops the use of itself and the code of the security module is based on parameters of the dynamic security module designated by the dynamic security module server device; and select and transmit one of said plurality of dynamic security modules to the security client of the user terminal and wherein the processor is arranged to transmit a different dynamic security module upon each transmission to the security client. a communication unit configured to transmit, over the network, the dynamic security module and to receive the security management event; and a processor configured to: control the communication unit; create a security session with a security client of the user terminal, wherein the security session is created by generating and storing a session ID and transmitting the session ID to the security client; store a plurality of dynamic security modules having different code structures or algorithms, wherein a first of the plurality of dynamic security modules varies in one or more variable portions thereof from a second of the plurality of dynamic security modules and wherein a part or all of said code structures or algorithms of each of said plurality of dynamic security modules has a predetermined validity period that limits its code's functionality at the user terminal, and each of the least two dynamic security modules is arranged to perform security management in the security client of the user terminal to protect the user terminal from malicious attack or infection of an application program with a virus and, when the validity period expires, the security module is configured to delete part or all of the code or stops the use of itself and the code of the security module is based on parameters of the dynamic security module designated by the dynamic security module server device; and select and transmit one of said plurality of dynamic security modules to the security client of the user terminal and wherein the processor is arranged to transmit a different dynamic security module upon each transmission to the security client. control the communication unit; create a security session with a security client of the user terminal, wherein the security session is created by generating and storing a session ID and transmitting the session ID to the security client; store a plurality of dynamic security modules having different code structures or algorithms, wherein a first of the plurality of dynamic security modules varies in one or more variable portions thereof from a second of the plurality of dynamic security modules and wherein a part or all of said code structures or algorithms of each of said plurality of dynamic security modules has a predetermined validity period that limits its code's functionality at the user terminal, and each of the least two dynamic security modules is arranged to perform security management in the security client of the user terminal to protect the user terminal from malicious attack or infection of an application program with a virus and, when the validity period expires, the security module is configured to delete part or all of the code or stops the use of itself and the code of the security module is based on parameters of the dynamic security module designated by the dynamic security module server device; and select and transmit one of said plurality of dynamic security modules to the security client of the user terminal and wherein the processor is arranged to transmit a different dynamic security module upon each transmission to the security client.