The invention relates to a protected slot machine system including means of paying by smart card (300), a smart card reader-validator (200) and means (360, 400) of managing the credits available for games. In order to prevent any fraud with respect to the sums of money actually won in the game, the system has control means (200, 450, 300) able to record, on the card (300) of a player, game-significant information (D) specific to the said card and able to effect a verification of this information.