US Patent 7636942 Method and system for detecting denial-of-service attack

A monitoring device monitors a packet transmitted to a communication device that is a target of the denial-of-service attack, and detects traffic abnormality information indicating an abnormality of traffic due to the packet with respect to the communication device. A performance measuring device measures performance of the communication device, and detects performance abnormality information indicating an abnormality of throughput of the communication device. An attack determining device determines whether the communication device received the denial-of-service attack, based on the traffic abnormality information and the performance abnormality information.