IT security experts have warned of a "major new malicious attack" that has been plaguing internet users since 2:00 GMT yesterday.

Sophos said that new variants of the Dorf family of malware, which had previously spread as breaking news of deaths caused by European storms, are now using disguises associated with love and greeting cards.

A wide variety of subject lines are being used in the spam campaign, including 'You're so Far Away', 'I Dream of you', 'Dream Date Coupon', 'Together You and I', 'A Bouquet of Love', 'So in Love' and 'Cuddle Up'.

Attached to the emails are files called 'flash postcard.exe' or 'greetingcard.exe'. When opened, the worm attempts to send itself to other email addresses found on the recipient's PC.

It also attempts to download further malicious code from the internet, designed to take over the computer and use it to send spam on behalf of hacking gangs.

"This attack is taking place against internet users right now around the world, resulting in a deluge of spam being relayed from innocent users' computers," said Graham Cluley, senior technology consultant at Sophos.

"People must learn to think before they click. It may be tempting to open an attachment which you think is a greeting card or a message from a loved one, but following your heart can get you into trouble sometimes.

"The best defence is common sense, combined with up-to-date antivirus software and email filtering at the gateway."