A new Sober worm is raising threat levels after luring fans through the offer of World Cup Football tickets.
At least three security companies are warning the bogus offer is spreading the virus quickly.
"Many people will be eager to attend one of the biggest sporting events in the world next year, and may think it is worth the risk of opening the email attachment just in case the prize is for real," said Graham Cluley, senior technology consultant at antivirus company Sophos. "Computer users who don't practise safe computing will feel as sick as a parrot, and will only be passing this worm onto other unsuspecting victims."
Next year's World Cup is being hosted in German and German-language versions of the email worm appear to be from football's governing body, FIFA. But when the user opens the attached file they become infected with the worm which sends a huge volume of emails, potentially slowing down company systems.
Finnish antivirus firm F-Secure said the worm has been found in the wild in many countries already.
The Sober worm has been back on the radar for a couple of weeks. In mid-April SC reported German and English language versions of the Sober worm email were spreading.