If I'm right I'm guessing it's something like Koobface virus. If this is the case then this one is easy to deal with. When you get a message from your friend on Facebook telling you that they've seen you on a video and to click a Facebook link to view the video, e-mail your friend back to see if they really did send that message, if not ignore it and tell your friend to check their system for the Koobface virus.
The Koobface virus works by sending you a link to the Facebook redirect cgi page which redirects you to another website outside of Facebook with a video which is encoded in a special way. It makes Media Player believe you need a new codec to watch the video, the codec is the Koobface virus, so Media Player downloads and installs the codec, installing the virus (which then goes in and sends messages out through your facebook account to all your friends and family telling them to view this video, it also installs a proxy so all internet requests go through the hackers computer, so he can block things out such as anti-virus websites/anti-virus updates, he can also take stuff such as passwords, usernames, credit card details, etc)