My sister clicked one of those stupid links people send with viruses, so know i'm sending them to all of my contacts, does anyone now how i can get rid of it?

I've un-installed Messenger, ran spy-bot, Ad-Aware and Norton, resolved any problems they found and then reinstalled messenger, but it's still happening.

Any ideas?

Whats it actually say to your contacts?

Try searching the Dodgy File's name in Google, with 'Removal' afterwards.
So, for example, I can think of two. One which states "Hey is this you in the picture" and a link, which links to the downloading of a virus. And another called a 'Block Checker' which automatically contacts all of your contacts asking them to download the Block Checker.
I do not personally know how to remove them, but if you try Google-ing them, that might work.

Look here.