You can take a look at this thread...this problem is an ongoing discussion. No one seems to be able to offer us much information. Maybe you can give us some. For example, what types of files have you downloaded recently? We don't want names, just file types and file sizes. This seems to be a new kind of malware...it isn't being picked up by antivirus apps, etc.
http://www.gnutellaforums.com/showthread.php?t=67151
Good Luck
Dano