Computer viruses are expected to cause damage costing millions of pounds during the Christmas period.

The latest bugs to hit computers around the world work in a similar way to the "I Love You" virus which ravaged systems last May.

Like the love bug, the newest nasties arrive as email attachments, this time with a festive theme.

One of the most prolific strains identified by industry experts has started to arrive in inboxes with the message: "Just testing email using Merry Christmas music file. You'll like it."

When the user opens the attachment, music.com, music.exe or music.zip, the virus displays a picture of Santa Claus and plays We Wish You A Merry Christmas.

The virus then emails itself to every address stored on the host computer.

One of the more vicious Christmas viruses arrives with the message "Snow White And The Seven Dwarves - The REAL Story".

When the user opens the attachment the virus displays an animated spiral on the screen.

It starts to infect files stored on the computer before forwarding itself via email to everyone in the user's address book.

Other nasty Christmas surprises identified by Sophos Anti Virus include a Spanish Christmas virus called Navidad which displays message boxes and deposits an evil eye in the corner of infected computer screens.

Graham Cluley, senior technology consultant at Sophos, warned computer users should be especially careful during the festive season and not open unsolicited email attachments.

"Some virus writers use the psychology of Christmas or sex as an enticement to people to open attachments when they would not normally."

"If you work in an office at Christmas it tends to be a bit like the last day of school, with people sending joke emails and screen savers.

"You never know if one of them might be virus-infected."

Viruses can cost businesses thousands in wasted time and effort when systems have to be shut down.

They stop computer programmes from running and corrupt data.

The full effects of virus infection may not be noticed for months after the initial strike.

Home users should also watch out.

Mr Cluley said: "If you have bought a computer for Christmas it would be very disappointing and potentially expensive to have it put out of action by a virus."

"Our advice to everyone is to use up to date anti-virus software and always practise safe computing.

"Think very carefully about opening up exe or word file attachments before putting your computer at risk."