The Trojan horse, a variant of IRCbot, arrives in an e-mail purporting to be an update to Skype, the popular Internet telephony application. Once opened the malicious software displays a phony installation error message. It then blocks access to security updates and installs a back door on computers, MessageLabs said in a statement.
The e-mail can have one of five different subject lines, which always refers to Skype. One, for example, reads: "Skype for Windows 1.4 – Have you got the new Skype?"
The e-mail body text advertises the Skype voice-over-IP application and urges the user to run the attached file to find out more, MessageLabs said.
