Patent ID: 7478425

Claim:
A server computer protection apparatus for protecting a server computer by allowing only proper access from one or more client computers to reach the server computer, comprising: an access request receiving unit that receives, in place of the server computer, server access requests sent from the client computers, wherein the server access requests each include, in sequence, a connection request packet, an acknowledgement packet, and a data request packet requesting the server computer to transmit data to the one or more client computers; an access request checking unit that checks each received server access request to determine whether the received server access request is improper, wherein the access request checking unit determines the received server access request to be improper when: the access request receiving unit does not receive the data request packet following the acknowledgement packet before a specific period of time elapses after the receipt of the acknowledgment packet, and the access request receiving unit has previously received at least one outstanding server access request in which a data request packet was not received following an acknowledgement packet within the specific period of time after receipt of the acknowledgement packet; an access request transfer unit which: transfers to the server computer only server access requests that are determined to be proper, and prevents the transfer to the server computer of server access requests that are determined to be improper; and a server load checking unit that checks whether a load on the server computer rises above a predetermined load, based on a ratio of the number of connection request packets and a number of times data is supplied from the server computer, wherein the access request checking unit determines that the server access request is not proper when the load rises above the predetermined load, to protect against distribution denial of service attacks.