With Valentine's Day almost upon us, computer users are being warned about the dangers of recurring socially engineered viruses.

Some of the most successful viruses over the last couple of years have used the promise of love to get users to set off the damaging electronic payload.

According to research firm Computer Economics, the 'I Love You' virus caused more than £6bn worth of damage to computer systems worldwide. Its wide dissemination through the internet was helped by the ingenuity of the email in which it was included.

Now a similar threat comes from the 'Valentin' virus, which sends messages to mobile phone users wishing them a happy Valentine's Day and directing them to a website.

On visiting the site, a file called 'loveday14-b.hta' downloads itself to a user's computer and creates another file containing malicious code in the Windows system folder.

The 'Matcher' virus is another example, this time enticing lonely hearts to find partners on the internet only to ruin the user's computer. The body of the message contains the text: 'Want to find your love mates!!! Try this, it's cool'.

Antivirus firm Sophos has warned against the use of electronic greeting cards that can potentially spread such viruses.

Graham Cluley, senior technology consultant at the company, said: "If someone sends you a Valentine's e-card, at best they're an unromantic cheapskate, at worst they're sending you a virus. Either way, you should probably consider ditching them.

"We advocate the old-fashioned approach: flowers, chocolates or a romantic meal for two. These gestures are much more seductive and don't carry any risk of infection."

Users are urged to keep antivirus software up to date and to scan all incoming emails even if they have apparently been sent by someone the user knows.