Just weeks after Facebook won an $873 million lawsuit against several people accused of hacking user accounts and spreading spam, the social networking site has to put up with another ordeal, as a new variant of the Koobface worm is hitting Facebook after previously having fun with MySpace users.

The virus is a worm that was discovered by IT security provider Kaspersky Lab, which said the threat, Net-Worm.Win32.Koobface.b, is targeting Facebook users through a message that goes “Hey, I have this hilarious video of you dancing. Your face is so red. You should check it out.”

This new version of the worm redirects a user “to one of many different compromised hosts, which displays a fake error message that the version of Flash is out of date.” The user is then prompted to download and open flash_player.exe, a new Koobface variant. This tricks users into downloading a file carrying the virus. An earlier version of the worm targeted MySpace users earlier this year but was quickly eliminated after new security measures were put in place.

Moreover if the viewer approves the Flash installation, Koobface attempts to download a program called tinyproxy.exe. This loads a proxy server called Security Accounts Manager. Koobface then listens to traffic on TCP port 9090 and proxies all outgoing HTTP traffic. For instance some victims report the bug has taken control of their browser, redirecting Google search links to other pages.

The easiest way to protect against the virus is to avoid opening unexpected e-mail attachments even when they seem to come from someone you know. Facebook has posted instructions about how to remove the virus on its security page as well. Should your PC be infected the Koobface worm, the Facebook security blog suggests resetting your password and running updated anti-virus software to purge the worm from your system. "Only a very small percentage of Facebook users have been affected and we're working quickly to update our security systems to minimize any further impact," the company said in a statement.

The virus watchdog blog for McAfee labs reports that Facebook is aware of the Koobface attack and is already working to remove the spammed links from its system. But with dozens of Koobface variants known to exist, McAfee warns that "the situation is likely to get worse before it gets better."

The virus was first detected in early 2008, but it's unclear how many of the social network's 120 million users have been hit with the virus.  Nevertheless it’s amazing how people still fall for this kind of strange messages. But maybe that’s why Koobface has had such a success. Because people just doubt it that someone still uses such a rooky infecting method nowadays.