Virus warning: Today's the day for Klez

Anti-virus companies are warning users to beware of an old virus with a very nasty sting in its tail which is timed to deliver its payload today.

The "E" variant of the Klez mass-mailing worm has been around since November 2001, but after a slow start is now riding high in the virus charts.

The worm is today timed to deliver the most painful part of its payload - the deletion of all files with certain extensions including .doc, .htm, .jpg and .mp3.

The problem is exacerbated by the fact the worm takes advantage of a vulnerability in certain versions of Internet Explorer which allows it to execute without users opening the attachment.

Network Associates has today raised the danger rating of the worm from a low" to a "medium".

Network Associates product marketing manager David Emm said: "Compared to something like Nimda this isn't as multi-faceted and hard to deal with, but it is still a danger.

"Just make sure your system is fully service packed, and that you've kept your anti-virus software up-to-date, and it shouldn't be a problem."

Most anti-virus companies have protected for the virus since its discovery at the end of last year.

However, if software isn't up-to-date the worm can be difficult to spot because of the random nature of its subject line and title.