While bots have been used to play the optimal strategy in other online card games, like blackjack, poker is a different animal. The biggest obstacles lie in the amount of information unavailable to the player and the need for the program to be able to employ a variety of strategies at different times, such as bluffing and laying traps for opponents, explained Billings, a doctoral student and master poker player.
“With chess – I don’t want to trivialize it – but it’s just a matter of calculation,” he said. “With poker, you really need to write a program that can think about the game and reason.”
The solution, in the case of the Vex Bot, was adding a layer of artificial intelligence over its ability to calculate probabilities.
“It will show you things that no human player has ever shown you before,” Billings said of the latest incarnation of the bot, which also has the ability to model its opponent’s behavior. “… One of the biggest advantages that programs have is that they have no fear, no shame. Humans can be intimidated. They will back off in the face of a very aggressive player. A bot will not. It has no compunction about doing whatever it will take to win. It will raise you with any two cards if it thinks that it has a very slight advantage based on your history. And it can induce a lot of anger and emotional upset. These things are ‘tilt monsters.’”
Rao, who served as one of the testers of Vex Bot, attests to its skills.
“It was a formidable foe,” he said of his initial encounter with the bot, before the addition of its new feature. “I can see that (the improved) bot, given enough hands, will become an absolute world beater.”
While the Vex Bot is undeniably at the head of its class, the mere existence of bots is a sensitive subject for operators of poker sites, all of which appear to have policies prohibiting their use.
...“If you’ve got a bot that can play 25 casinos, two tables apiece, even if you’re playing a (mid-level) $10/$20 game … that’s $1,000 an hour,” he said.
And if such a bot is created, how long will its author be able to keep it secret?
“It’s only a matter of time before a talented poker player who also happens to be a good developer decides she or he wants to be remembered as the author of the first bot that changed online poker forever,” an author who goes by the screen name “loic” lamented recently in the Twoplustwo.com poker forum.
More insidious, teams of bots playing at the same table and using out-of-band communication have an even stronger advantage. Even if most online games are not yet bots vs. humans, I imagine a lot of players are using poker software for strategy while playing online. (This is called "freestyle" play in chess.)
See related Wired article.