A new wave of emails with 'sulfnbk.exe' in the subject line are being sent to users - and this time it may actually contain a harmful virus.

Last week, a hoax email warning people that their PCs might contain a virus duped an untold number of users into deleting the sulfnbk.exe file from their hard drives.

Now, on the back of the wildly successful virus hoax, antivirus firms are warning that a second variant of the email may actually contain a virus itself.

The new variant carries a harmless version of the 'sulfnbk' executable as well as the infamous Magistr virus. Earlier warnings have already pegged Magistr as one of the nastiest pieces of so-called malware ever written.

The virus is dangerous, not just because it is capable of completely overwriting a hard drive, but because it can also erase the CMOS as well as destructively flashing the BIOS, leaving the affected computer in need of a BIOS chip replacement at the very least.

Before the Magistr virus releases its deadly payload it emails itself to all addresses found in Outlook and Netscape address books, with a random subject line made up of text found on the hard drive along with a random file.

In this case, the subject line turned out to be 'sulfnbk.exe' and the attached file was 'sulfnbk.exe' - a spookily timely coincidence that could have propagated the spread of the Magistr virus had antivirus companies not released signature files for this particular nasty back in March.