Is your computer cheating at online poker?

Is that a card you've got up your mainframe?

A new computer malware allows users to cheat at online poker. Here's how it works: the victim becomes infected with the malware, usually from a website or while downloading some other piece of software. Once infected, the malware sends screen shots of the victim's computer screen to the attacker. That allows the attacker to see what virtual poker table the victim is playing at, follow him or her there and then see his cards. The malware is targeted specifically at the world's two largest online poker sites, PokerStars and Full Tilt.

ESET, an IT firm in Slovakia, was one of the first to write about this malware. Robert Lipovsky, senior malware researcher at ESET, tells CNBC there have been more than 1,000 documented cases of these malware attacks since March, mostly in Russia and Ukraine.

But PokerStars, a unit of Amaya, tells CNBC, "There have been no claims of attacks against the PokerStars or Full Tilt servers."

PokerStars security also offered this advice to its users: "We recommend that players protect themselves against this sort of attack by practicing good computer security. Players should keep their operating system updated, use reliable antivirus software, and only install software from reputable sources."

But in the highest-stakes games, players can play heads up (one-on-one) tournaments for thousands of dollars. And this kind of malware would work best against just one opponent. So in other words, the higher the stakes, the bigger the potential reward. One wonders if a threat like this will be enough to force players to stay away from the big-money matches.