Britain's leading bookmakers were all targeted

Three men were seized in Russia after a police operation involving specialist crime units from Britain, Russia and four other countries.

The men were part of a global extortion racket which began in October.

It targeted the websites of British and other bookmakers, causing the firms millions in lost business.

Maximum disruption

The gang bombarded bookmakers' computer servers with thousands of requests for information - "denial of service" attacks - designed to paralyse them and prevent other users from being able to access the sites.

As a result, some leading betting websites ceased operating and were unavailable - sometimes for short periods but in extreme cases, for several days.

Companies targeted included high street bookmaking chains such as William Hill, Ladbrokes and Coral and internet betting exchanges such as Betfair and BetDaq.

Websites were attacked in the run-up to major sports betting events such as the Cheltenham Festival, the Grand National and the Six Nations, when betting turnover was at its highest.

The gang then demanded payments of up to $40,000 (�21,000) in return for stopping the attacks.

How blackmailers tried to attack the Grand National

Bookmakers were forced to invest heavily in new technology to defend their websites from attack.

A spokesman for the Association of British Bookmakers welcomed the arrests.

"We're very pleased with today's developments," he said.

"British bookmakers were targeted by these attacks, and anything which causes downtime for the businesses is not something that the companies could take lightly."

The National High-Tech Crime Unit, which led the investigation, tracked down the racketeers by tracing money transfers between the three men and ten gang members who had been arrested in Latvia in November.

Money trail

The gang, whose members operate across eastern Europe, has previously attempted to sabotage betting websites in the US and the Caribbean.

A NHTCU spokeswoman said the arrests were only the first step in tackling organised crime in the area.

She said: "We don't know if there is another gang out there although this will provide an incentive not to do it. Organised crime will always chase the money and if it sees an a easy way of getting it, it will take the opportunity."

Russia's Ministry of Internal Affairs assisted in the investigation as did liaison officers working for Customs & Excise in Russia, the Central Asian Republics and the Baltic States.