Worm warning: Frethem's running free and spreading fast

A new family of email worms that can spread without users even clicking on an email attachment has been discovered in the wild.

The worm, called Frethem, does not carry a dangerous payload, but is already spreading quickly.

Anti-virus firm MessageLabs rate it as the eighth most prolific virus in the last 24 hours.

Users can spot Frethem by the subject line "Your password!" and the message body: "ATTENTION!/You can access very important information by this password/DO NOT SAVE/password to disk use your mind/now press cancel."

However the worm is programmed to spread when the email is opened, meaning users do not have to click on the attached file to spread the worm.

It manages this by exploiting a well-known vulnerability in Microsoft Outlook email software which is still unpatched by many.

Sophos said it had found six variants of the worm, one of which it found in the wild.

Trend Micro said it rated the worm a high risk. Concerned users can find analyses of the worm at http://www.sophos.com/virusinfo and http://www.trendmicro.com/vinfo/ .