It sounds like you have a worm. Try the easy fix mentioned at the end of point 2 here...it's worked for a lot of people.
WARNING: Viruses on the network you should be aware of

If that doesn't work, there are links to help sites in point 5. Norbiesworld has helped a lot of LW users, but at the moment there's a very long wait for a reply there.

Always make sure that you're using a good AV program. Keep it updated & use it to scan files that you download before you open them