Download a new virus program (freebie) and run it, it may have just been a script kiddie doing remote admin (like someone else said its MSN)or it could be a legit virii and "tweaked" norton not to recognize it. www.vcatch.com version 5.0 should do. Try this. If you still notice problems, use some intrusion detection software: http://www.fidelissec.com/mudpit.html (never heard of this one just came across it recently though) www.snort.org (decent though this mudpit thing above is supposed to be better) http://www.javaspot.net/cids/ If its someone remote admining your comp then you have numerous options to "rectify" their bad behaviour.
Dunyain
Edit: You should try the removal tool also, don't know if you have, you just stated you've downloaded it and thats it. I was under the impression that this new "worm" went into *higher* (couldn't think of the correct word) level microsoft programs
2nd EDIT: Do you have any experience with PCAnywhere or any other remote admin program?? That's kinda what it sounds like, when you connect from a remote location, some programs do that (aforementioned one specifically) so that you know that there is a remote admin. did your Background CHANGE?? If so, it sounds like someone was/is trying to remote admin your computer.