To be sure, I deleted this file. In view of subsequent warnings about a hoax, I re-installed windows, and the file has been replaced. Therefore, I consider it safe to assume sulfnbk.exe is bona fide,
It is a hoax, although how the hoax messages are generated I'm not sure.... Check the Symantec site at: http://securityresponse.symantec.com/avcenter/venc/data/sulfnbk.exe.warning. html It tells you