Shadowserver.org, a watchdog group of volunteer security professionals who track and report on hacker activity, noted the Distributed Denial of Service attacks on their Web site this week.

The report listed more than 30 gambling sites attacked in the past week, the majority with Russian Internet addresses, but also including U.S. companies and one British site.

"Some were attacked for a few hours and others for a few days. … The desired result of the attacker is to completely disrupt service to the Web site," reads the report. It noted that several of the sites being attacked were "fully unavailable for the last few hours."

News and discussion sites for online gamblers noted that several poker sites were hard or impossible to access at various times over the past few days.

Also on the list of sites being targeted by the botnet of computers compromised and covertly controlled by hackers were services for Internet hosting, Web advertising and e-payment.

The motive for the attacks was unclear, Shadowserver.org said, adding that details of the hacked server that was providing targeting information to the botnet had been passed to the company owning it, who had shut down the attack for the time being.