A new virus which first appeared just before Christmas is infecting thousands of computers across the world.

The spread of the Windows e-mail worm, called Yaha.K, has led anti-virus firms to classify it as a high risk.

The virus has now been reported in 100 countries, predominantly in the UK and the Netherlands, according to MessageLabs which scans messages for viruses.

It spreads by e-mailing itself to everyone in your address book. It may also try to shut down anti-virus programs.

Computer users are being advised to delete any suspect e-mails they receive, as well as updating their anti-virus software.

Love and hate

The virus is a version of the Yaha worm which first appeared in February.

Yaha.K subject lines

Are you in Love You are so sweet Shake it baby Sample Playboy Wanna Hack ?? Free Screensavers Need a friend? Free Win32 API source Wanna be a HE-MAN One Hackers Love

The new one was first spotted in an e-mail from Kuwait on 21 December. Since then, MessageLabs says it has stopped 33,487 copies of the virus.

Yaha.K arrives in an e-mail disguises as an .exe or .scr attachment, with a variety of subject lines and messages related to hacking, love, hate and porn.

The terms used in the subject line include Sexy Screensavers 4 U, Wanna be my sweetheart? and The Hotmail Hack.

Virus plague

The worm raids the Windows address book to e-mail itself to your contacts, forging e-mail addresses.

It may also try to shut down security-related software, such as firewalls and anti-virus programs.

Anti-virus firms say the worm may also launch a denial of service attack against a Pakistani Government website, infopak.gov.pk.

E-mail viruses have plagued computer users throughout the year.

Figures from MessageLabs show that one in every 212 e-mails containing a virus in 2002.

This reflects a big increase on previous years. In 2001, the firm stopped an average one every 380 e-mails, while in 2000 the figure was as low as one every 790.