The Sober-N worm, which uses a number of different subject lines and messages to lure users into opening attachments, has been reported in over 40 different countries.
Once installed in a machine, the worm mails itself to addresses harvested from the hard drive.
Some messages are sent in English, and refer to passwords, mailing errors and registration confirmations, but others are written in German and offer tickets to the World Cup – an offer that many have found too attractive to resist.
Part of the worm's success appears to be down to timing: it first appeared on Monday, the day that the second sales phase for World Cup tickets opened for business.
The organising committee of the World Cup has issued a general warning, advising fans not to open any attachments connected to e-mails purporting to come from FIFA. Those applicants who are successful in the second phase are notified by an immediate on-line confirmation.
Those applicants who successfully bought tickets in the first sales phase were notified by e-mail on 22nd April, before the worm was released.
"Many people will be eager to attend one of the biggest sporting events in the world next year, and may think it's worth the risk of opening the e-mail attachment just in case the prize is for real," said Graham Cluley, senior technology consultant for 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."
The advice, as ever, is not to open attachments and to ensure that your anti-virus protection is up to date.
