Skype users are warned to be on their guard, regarding malicious instant messages that have been sent through the service, designed to infect Windows computers.

A malicious worm is taking advantage of the Skype API to spam out messages similar to the one below:

lol is this your new profile pic? http://goo.gl/[REDACTED]?img=[USERNAME]

Clicking on the suspicious links leads to the download of a ZIP files (variously called skype_06102012_image.zip or skype_08102012_image.zip) that contains executable files  as Troj/Agent-YCW or Troj/Agent-YDC.

The Trojan horse opens a backdoor, allowing a remote hacker to take control of infected PCs, communicating with a remote server via HTTP.

On execution the malware copies itself to

%PROFILE%Application DataJqfsfb.exe

and sets the autostart entry as below:

 

 

Before you know it, your computer has been recruited into a botnet (the malware is a variant of the Dorkbot worm) and could fall victim to a ransomware attack.

There have been many variants of the Dorkbot attack spotted over the least year or so, spreading via Facebook and Twitter. The threat can also spread via USB sticks, and various instant messaging protocols.

Always remember to be suspicious of unsolicited out-of-character messages sent to you by your online friends.

Credits: http://www.sophos.com