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 you need more help, there are links to help sites in point 5 of that thread. Norbiesworld has helped lots of LW users, but at the moment there's a long wait to have questions answered.

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