Hi just because, it sounds like you've picked up something, maybe Norton hasn't detected it, I noticed you said that you never opened the zipped files...Im curious to know the size of the file that has caused this to happen...

Run this AV scan http://housecall.trendmicro.com/

This thread has information about the same problem and offers advice on fixing it...
http://www.gnutellaforums.com/showth...keep+appearing
Let me know how you go with this....