A virus called Koobface is spreading through Facebook and MySpace. The worm is targeting users with messages about Christmas, which then link through to a fake Facebook video or Facebook page.
The messages are accompanied by the phrase "I can't fall asleep after viewing this video. I haven't seen anything like this", with some variations of spelling. When clicked, it brings up a fake page with a Christmas-themed video and a file called setup.exe is then offered, sold as either a free antivirus or Flash Player upgrade.
The file is currently detected by 16 out of 41 antivirus products, claims monitoring agency VirusTotal. If infected, the worm logs into Facebook, MySpace, and a few other social networking sites, sending similar messages to all your friends on the network.