William Hill is the latest victim of a cyber extortion wave targeting gambling Web sites, this time hitting the bookmaker on the eve of this week's Cheltenham horse race festival.
Britain's second-biggest betting chain was hit by a barrage of data which disrupted its gambling Web site on March 11th.
"We were targeted, but were able to take the appropriate action to minimise the nature of the disruption," Graham Sharpe, a William Hill spokesman said today.
Police and computer security experts say organised crime is behind the growing crime wave, which typically intensifies in the days leading up to the biggest sports events of the year.
The culprits targeted a variety of sites before American football's Super Bowl in January, each time demanding money or threatening to take out the sites with a crippling data barrage.
And gambling sites have been on red alert with today's start of the three-day Cheltenham horse festival, kicking off one of Britain's biggest betting weeks of the year.
Police call it the age-old protection racket with a cyber twist. And, the crime wave is getting worse, authorities said.
"The level of intensity is higher than any we've seen before. They are increasing the force and frequency and sophistication in these attacks," said Mr Richard Starnes, director of incident response for Cable & Wireless, one of the largest Internet service providers (ISPs) in Britain.
Many ISPs are working with victimised sites and law enforcement to track down the culprits as larger and larger sites have been taken out for longer periods, experts said.
Both police and security experts believe gangs in Eastern Europe and Russia could be behind some of the attacks.