On December 4, rumor started to spread about a worm attacking Facebook, although the malicious code has been spotted as early as August this year. Nevertheless, now the virus has been changed so that it only attacks the social networking website and it appears that it’s doing the job quite rapidly.

Koobface is able to spread quickly because it uses messages that seem to come from friends of those who have accounts on Facebook in order to travel through the site. These messages feature subjects such as “You look so funny on our new video” and contain links to websites that apparently host movie clips. When a Facebook user who has received one of these messages tries to watch the video clip and thus clicks the aforementioned link, he or she is told that Flash Player is needed to view the file. Consequently, if the person chooses to download the software, they actually download a file containing the malicious code.

A version of Koobface has attacked social networking website MySpace earlier this year, but the weakness was fixed through enhanced security measures the website briefly took.

Currently, Facebook urges users on their Security page to appeal to the latest anti virus software and also to change their passwords in case the virus has affected their computers.

Moreover, the website has begun resetting passwords pro-actively and sending its users e-mails warning them they might have been attacked by a virus.

Until now, no information on how many of the Facebook users have fallen prey to the Koobface malicious software has been given out.