Koobface, a new worm quickly spreading on Facebook that travels through messages which appear to come from your friends. The messages carry subject lines like "You look so funny on our new video" and it contains a link to a video site that appears to contain a movie clip. If the user attempts to watch the clip a message says the user needs to load the latest version of Flash Player in order to play the clip. This usually tricks the user into download the file which contains the malware.
It's still unclear how many users have been affected by the virus but Facebook security is asking users to use the latest antivirus software and change their passwords if they've been affected. The company also appears to be resetting passwords pro-actively and notifying users about the possibility of having a virus on board.