Guillaume Lovet, Threat Response team leader at Fortinet, said: "One of the easiest and quickest ways to make money on the internet is setting up an auction on eBay for a [bogus] item, cashing the money, then disappearing.

"However, your account is likely to be closed because of the buyer complaints. You could create a new one but people generally do not buy an expensive item from a brand new account. Hence the value of stolen eBay accounts."

Fortinet also reported that the Sober worm topped the virus charts in December, with over half of all infections attributed to the 'AD' variant.

But in more worrying news the company found that one in 20 MMS messages sent via mobile phone were infected with the Commwarrior virus, suggesting that this malware may be more widespread than first thought.

The finds were made after Fortinet installed an antivirus filter for a mobile phone company in Germany.

Commwarrior was first spotted in March and has since appeared in isolated outbreaks around the world.

The virus tries to spread via Bluetooth between the hours of 8am and midnight, then stops these attempts and sends itself to everyone in the phone's contact lists via MMS until 7am. In the remaining hour it seeks to wipe all evidence of its activities.