Skype Trojan Poison Ivy Spreading

Hijacked trusted and legitimate Skype accounts are invaluable from a social engineering perspective. Trust is vital, even novice end users know it. If the cybercriminals were to automatically register thousands of bogus accounts, they would attempt to only target users who allow the receiving of messages from users who are NOT on their contact list. Although millions of Skype users continue receiving these messages, the majority of successful malware campaigns using Skype as propagation vector, tend to involve trusted and compromised Skype accounts in an attempt to increase the probability of a successful infection.

Source: Poison Ivy trojan spreading across Skype