C2 via Social Networks
Although some malware can work on its own, many samples are programmed to stay in contact with the attacker for instructions for use. The mechanism these robots use to communicate with their operators is called command and control (C&C or C2).
C&C channels can take the form of IRC chatter, peer-to-peer protocols, generic HTTP traffic, etc. Several recent malware samples also used social media for C&C.