How do I get rid of a facebook virus?

I have had my facebook for a year and never had any problems with it until today I noticed when I logged in I saw an IM window from last night when I was talking with my friend. It had one extra message at the bottom of the window that read, "Hey there..saw you on here...you should look at this!! www.b2kwm.tk" The chat window said I had typed it but I don't remember typing it!!! I went to the link and it said, "page not found." I wasn't sure what it was but then 5 minutes later it said I had written on a bunch of people's walls and I never did! The message posted on the walls read, "alot has been said about this diet and i am walking proof that its amazing, dont believe me? check this out. enjoy..www.whvf3.tk." It posted that to 12 of my friend's walls and I never wrote that to anyone's wall! I just changed my pword but is that enough to stop the virus? Does any one know what the name of the virus is, what causes it, and if it's harmful to my computer and other internet accounts? Any help would be greatly appreciated! Thank you!