A method of inhibiting the spread of malware across a network of interconnected computer terminals. The method includes detecting malware or suspicious behavior at a first computer terminal and inspecting the first computer terminal, before and/or after said step of detecting malware or suspicious behavior, to identify contacts forming part of a social network. Identities of the identified contacts are sent to a backend security system, and at the backend security system, said identities are received and instructions sent to one or more second computer terminals associated with respective identities to cause those second computer terminals to implement an increased level of security.