Specifying system, specifying device, and specifying method

A specifying device receives detection information from a security device that detects hacking into a network or an activity of a terminal related to infection, and specifies a state of the terminal from information of the terminal and content of activity of the terminal included in the detection information. The specifying device specifies, when specifying that the terminal is in the state of being infected with malware, a terminal that may be infected before performing the content of the activity of the terminal included in the detection information based on connection information stored in a configuration information storage device, and specifies a terminal located on a route, along which the infected terminal is likely to be used for hacking or for infection of the terminal in the future, as a candidate for an infected terminal likely to be infected.