Did you read the link that FOTH left?

Go back to it. At the end of point 2, there's a link to an easy fix for LW popping up...try that one. It's worked for lots of people.

If you're stuck, see point 5 for info about help sites. Try Norbiesworld.

You need to make sure that you're using a good anti-virus program. Keep it updated & scan all files that you've downloaded before you open them.