Worm on Windows Live Messenger

Hello!

I turned on my msn this morning to find one of my friends had send me this while offline:

Tony and Linda just told me to try these pills I saw at their place, Acai berry. They get them for $5 and they swear they lose weight. 11 pounds in two weeks they said. Anyways, I ordered up a bottle from the offer I found here: http://muchjust.com

She said that several other people have received the same message, and she doesn't know where it came from. I figure it's a worm, and probably everyone on her contact list recieved the same message. She hasn't downloaded anything by the way of pictures, etc, off of msn recently.

She's running Windows Vista with McAfee Firewall, has run several virus scans and it found nothing. There is no other apparent problem other than the sent messages. Last night everything was fine, then she signed off msn and shut off her computer. She logged back on after 9 (password worked fine, and everything), and found several contacts telling her about this message... the timestamp on my copy of the msg says 8:44.

So, any ideas on how to get rid of this thing? I can get more details if you need them, we'd just like to be able to clean up her computer.
Thanks! :)