Spammers have launched a pump-and-dump campaign that attempts to manipulate share prices by delivering a message in an MP3 music file.

IT security firm Sophos said that emails are arriving with an attached MP3 file purporting to be a song from well-known artists such as Elvis Presley, Fergie and Carrie Underwood.

The files actually contain a monotone voice encouraging people to buy shares in an obscure Canadian company.

The subject line and body of the emails are usually blank, and typically contain an attachment called 'hurricanechris.mp3', 'allforone.mp3', 'carrieunderwood.mp3', 'elvis.mp3', 'baby.mp3', 'fergie.mp3' or 'bbrown.mp3'.

The voice on the MP3 file, which is randomly altered in an attempt to avoid detection by anti-spam filters, says the following:

'Hello, this is an investor alert. Exit Only Incorporated has announced it is ready to launch its new [obscured].com website, already a huge success in Canada, we are expecting amazing results in the USA. Go read the news and [obscured] on EXTO. That symbol again is EXTO. Thank you.'

Exit Only is a Canadian company that runs a website marketplace for new and used motor vehicles.

Graham Cluley, senior technology consultant at Sophos, said: "Users may click on the MP3 file expecting to hear Elvis, but they'll be all shook up when they discover it's actually a voice resembling Marvin the Paranoid Android droning on about a stock that is set to be the next big thing.

"The spammers are already likely to have purchased stock on the cheap, and are now trying to artificially inflate its price by encouraging others to purchase more.

"Once the stock rises, they'll quickly sell up, leaving the duped investors crying in the chapel. Thankfully though, it's hard to believe that many internet users will fall for such an amateurish presentation of an 'investor alert'."

Cluley advised companies to consider banning these sorts of file by default, as they can create legal as well as security headaches.

"Although the spammers seem to have a fair bit to learn about machine-generated sales patter, some companies might consider blocking all MP3s in email as a matter of course," he said.

"So many music files infringe copyright, and it can be hard for a company to establish which ones are legal and which are not after they have arrived.

"Blocking MP3s, or at least quarantining until requested by the user, can be a good way for a company to take a proactive stance against the use of email for illegal file sharing. It also has the benefit of neutralising this sort of spam at the same time."

Pump-and-dump stock campaigns account for approximately 25 per cent of all spam, according to Sophos, an increase of just 0.8 per cent since January 2005.