Computer users are being warned about a new virus which is spreading via e-mail.

The virus, called Yaha.K, is a mass mailing worm affecting computers running Windows which first appeared on 21 December.

Since then it has spread quickly, leading the anti-virus firm F-Secure to give it their second highest danger rating.

People are being advised not to open any e-mails which have attachments ending with .scr, .exe and .com.

'I Love You'

Yaha.K is a new version of the Yaha worm which first appeared in February.

It is relatively harmless, compared to more destructive viruses.

It can compromise a computer's security settings by stopping anti-virus programs and shutting down firewalls.

The new variant looks for e-mail addresses in Windows Address Book and sends itself to all the addresses it finds.

In an attempt to trick people, the virus composes several different types of e-mails, using subject lines such I Love You, Patch for Klez.H and Free Demo Game.

Growing threat

MessageLabs, which scans e-mail messages for viruses, said it first detected the worm in Kuwait.

It has now been spotted in 96 countries, predominantly in the UK and the Netherlands.

Overall the company has blocked 21,295 copies of the worm so far.

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, MessageLabs stopped an average one every 380 e-mails, while in 2000 the figure was as low as one every 790.