How to get rid of Koobface Virus if I’m already infected?

I have stupidly clicked on a link that said "Check out this video chat are you doing in it?" in a chat on Facebook. I was even forced to update my Flash Player but there was no video. This frightened me and on doing a Google search, I found out that I have been attacked by the “Koobface” virus! I want a way out of this. Please help me disinfect my PC, because the antivirus is proving useless!
