I once got an infected flash drive to clean. As soon as I put it in, Norton told me it had w32.sillyFDC. I tried to delete it, but the drive was locked. So i unlocked it and put it back in, and the virus disapeared right in front of my eyes. So I scanned it with Norton and it picked up 3 instances of w32.rontok@mm. But even a regularly updated Norton '07 can get confused by this old tricky virus. It names itself X.exe where X is the directory in which it resides. If you open the folder X in Windows explorer the virus moves itself, too quick to catch. I was eventually forced to delete 19 copies of it in dos prompt.
