It's a virus. Point 4 here deals with it
http://www.gnutellaforums.com/showth...threadid=41432

You need to be really careful what you download. Make sure you have a good, up to date AV program & scan a file before you open it. There's good advice in the thread, also a link to norbiesworld. If you can't get rid of the virus, he'll be able to help you