"It was only time before we started seeing hackers taking advantage of the fun and festive time people are having around the World Cup," said James Rendell, senior technology specialist at Internet Security Systems.

"We suspect that this is only the start of things to come."

Celebrity appeal

Malicious coders often take advantage of celebrity names or large news events to spread viruses and worms.

Last year, an e-mail scam offering regular news updates following Hurricane Katrina spread a virus that allowed hackers to take control of a computer user's files.

The World Cup is particularly attractive to hackers.

"Millions of people worldwide are following the World Cup and will be using the internet and e-mail to keep up to date with all the action," said Graham Cluley, senior technology consultant at security firm Sophos.

"In the past, we have seen viruses exploiting the popularity of celebrities like Anna Kournikova and Britney Spears; Ronaldo, David Beckham or Wayne Rooney could be next," he said.

In 2005, another worm, known as Sober-N, spread via e-mails that claimed to offer tickets to the World Cup.

Once a machine was infected, the worm downloaded software that tried to turn the computer into a spamming machine.

Earlier this year, a spam e-mail that offered a wallchart for the World Cup contained a Trojan horse that allowed hackers to take control of a user's computer.

Nude footballers

The latest threat uses a variety of different e-mails to spread to different machines.

Common subject lines include "Soccer fans killed five teens" and claim to come from US news organisation CNN.

Others tempt people with pictures of nude soccer players.

The e-mail reads "Nudists are organising their own tribute to the world cup, by staging their own nude soccer game, though it is not clear how the teams will tell each other apart. Good photos".

Once a user has opened the e-mail message, the Sixem-A worm automatically downloads software that disables a user's security settings.

It also harvests e-mail addresses so that it can continue to spread.

Security firms have now developed a patch for the worm but advise windows users to remain vigilant for the rest of the tournament.