The UK's National Hi-Tech Crime Unit has worked with Russian authorities to smash a racket responsible for extorting thousands of pounds from online sport bookies.

Three men were arrested in St Petersburg and south west Russia on Tuesday following months of collaboration between the NHTCU and Russia's Ministry of Internal Affairs computer crimes department.

Bookies have been hit with denial of service (DOS) since October 2003, with cyber criminals bringing web sites down by bombarding servers with thousands of messages in a bid to extort money from them.

The gangs, which have cost firms millions of pounds in downtime, then blackmailed bookies by email, demanding money in return for a stopping the DOS attacks.

'Thanks to the response of all the parties involved, we have helped to dismantle a determined group of organised criminals,' said Detective Chief Superintendent Len Hynds, head of the NHTCU.

'The more we work together in the fight against organised crime, the safer the UK will be for business,' he said.