This is a hoax. The sulfnbk program is a necessary part of your computer (something to do with file names). Before forwarding Virus warnings, check out this website: Click here: Symantec Security Response - Hoax Page . If you scroll down you'll see the Sulfnbk.exe virus hoax is listed. There are instructions at the end of the Sulfnbk description for restoring the file if you did delete it.