I've had it, probably got it off Kaaza or e-mail.
It's a backdoor trojan. It could also be hidden or other trojans being hidden..
Search for these files and delete them if you have them.
hiddenrun.exe
hiderun.exe
Then...
DL TDS-3 (free DL) and update it (update file at bottom of page). Then do a full scan. It will take a while. delete suspect files.
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Norton is poor with trojans. forget it.