Koobface Worm

Facebook has partnered with Microsoft to combat the Koobface virus. Facebook is a very popular social networking website. It is free for users.
Koobface is a virus that spreads through malicious Web links and affects Facebook and MySpace users running unpatched versions of Windows. Once your computer is infected, it steals social networking logon information to create spam messages and sends them to your friends on Facebook or MySpace. It wants you to download files so it can continue infecting other computers through social networking.
Microsoft teamed up with Facebook to add Koobface to its Malicious Software Removal Tool to remove Koobface from nearly 200,000 times from over 133,677 computers in more than 140 different locales around the world, said Jeff Williams, a principal group program manager for the Microsoft Malware Protection Center.
As Williams notes, Koobface is highly polymorphic, meaning that it's constantly changing to look like something else. So far, he said, there have been more than 20,000 Koobface variants. This, incidentally, is why signature-based malware detection alone is no longer sufficient to protect computers.
So if you don't trust the site then don't download it. Make sure you run virus scans to protect your computer from viruses.
http://www.informationweek.com/news/security/vulnerabilities/showArticle.jhtml?articleID=216403016&subSection=Cybercrime