With the World Cup about to kick off, virus experts have warned computer users to be on their guard against infection.

With millions of people using e-mail and the internet to keep up to date with the soccer action, anti-virus firm Sophos says screensavers, spreadsheets and electronic wall charts could prove ideal hiding places for viruses and worms.

"We have already seen viruses utilising the popularity of celebrities like Anna Kournikova and Britney Spears," said Graham Cluley, senior technology consultant at Sophos.

"David Beckham or Michael Owen could be next. Amid the enthusiasm for the competition, it's important that users maintain a solid defence," he added.

Experts say the danger from these hidden viruses is most acute in the office, as employees are often the weakest link in computer security systems.

Employees are the enemy within

Jeremy Butt, WatchGuard

Malicious attacks on computer networks from employees are on the rise but often people expose their workplace to virus infection without even knowing they are doing it.

"On the average server, there are 30,000 things that can be changed. Not everyone is a malicious employee but just goofing around trying to improve things," said Jeremy Butt, head of internet security firm WatchGuard.

"Employees are the enemy within and are often the weakest link for security," he added.

Education crucial

According to a government survey, nearly half of large companies have experienced security incidents in the last year that were related to employee web access.

But only a tiny percentage say that they have put any resources into educating employees about security.

Only one in 10 has any kind of computer forensic procedures to identify the source of a breach.

"By the time they have discovered it is a security threat, they have destroyed the evidence," said Chris Potter, one of the co-ordinators of the government survey.

Disastrous consequences

Experts say the key is to educate people in the dos and don'ts of computer security.

"It is often assumed that people know how to use the network securely on day one of a new job but that often isn't the case," said Mr Cluley.

As computer users become more sophisticated, they bring the knowledge they have gleaned from using their home PC into work, often with disastrous consequences.

"It is relatively trivial to set up instant messaging software and then you could be spreading all sorts of information and files around, including pornography, racist material and viruses," said Mr Cluley.