There's always some unknown message pop out from ur friend saying that "view who blocked you" , "come and see my new album " and so on so on...some of them make it too late after clicking the link and give out every single details they have to the so-call a message from your friend..

but later they found out that's a virus , but they got no idea what to do...just leave it there and let the message spread around again...

There's a very simple to make this virus out of your account , simply change your msn account password..and that's all done..

I am not sure that this work for all , but if u remember the website that u visited which have virus request for your msn username and password it most probably will turn out fine after u change the password..