A detecting apparatus generates a collection of events, the collection being formed based on a predetermined condition, from events obtained for each identifier identifying a terminal in a monitoring target network or a piece of malware. The detecting apparatus then extracts, from a cluster formed of collections of events, the collections having a similarity therebetween equal to or larger than a certain similarity, events commonly appearing in the collections of events belonging to the same cluster, and extracts, according to a predetermined condition, the taken out events as a collection of detection purpose events. The detecting apparatus then detects that a malware infected terminal is present in the monitoring target network, if a generated collection of events based on communications in the monitoring target network is determined to match the extracted collection of detection purpose events.