Yes, and no.
The movie is fictional. It didn't actually happen.
But it is fact based. There was a superuser scandal on Absolute Poker and Ultimate Bet that the movie is "loosely" based on. Ivan Block (Ben Affleck) is loosely based on the management at AP and UB who used superuser programs to win millions of dollars from their players by seeing the hole cards.
But as far as I know, no one actually traveled down to the headquarters, confronted them, and started working for them.