Shoutbox

I believe this is a virus and I don't know how I got it. It appeared randomly one day and it continued on. What happens is that whenever I log into Windows Live Messenger, a conversation pops up with the name "WebCamCHat" and a random person is talking. There isn't even an email I can trace so that I can delete/block it. Here's a picture of it. I hope there's a solution, thanks!