A worm posing as a Valentine greeting is spreading fast across the internet.

The Dref-AB worm has been deliberately timed so office workers and home computer users to find the malicious email in their inbox first thing this morning.

Since midnight GMT, the Dref-AB worm has accounted for 76.4 percent of all malware sighted at Sophos's global network of virus monitoring stations.

'This new Valentine attack is spreading hard and fast across the net, accounting for over three quarters of all the malware we've seen at email gateways around the globe since February 14 began,' said Graham Cluley, senior technology consultant at Sophos.

Subject lines used in the attack are many and varied, but all pose as a romantic message. The worm is attached to the emails in files called flash postcard.exe, greeting postcard.exe, greeting card.exe, or postcard.exe.

'Cynical hackers are using the theme of Valentine's Day to conquer innocent people's computers and use them for their own money-making purposes,' said Cluley. 'Your PC and the data on it is precious, and it needs to be protected. No-one should be blinded by the excitement of Valentine's Day into opening unsolicited attachments or clicking on links to unknown websites, as you could be falling deep into a hacker's trap.'

Opening the attached files on a PC activates the worm, which then sends itself to other email addresses found on the now infected computer.

The worm code is designed to download further malicious code from the internet in an attempt to take over the PC, convert it into part of a zombie network, and use it to send spam on behalf of hacking gangs.

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