In an astonishing turn of events, it appears as though Russian hackers have actually engineered (if you will) a method for gaming the system when it comes to slot machines. Since 2014, possibly earlier, some casinos have been noticing larger than normal payout amounts. Even though the various slots in use did not show any signs of tampering or malware, the pattern of large payouts from otherwise sound and working machines was unmistakable.

Casinos Have No Fix?

Through careful observation of surveillance tapes, investigators have determined that the culprits were able to commit their heist without actually installing any software of their own on the systems in questions. In fact investigators found that there was no tampering with any hardware or software at all, leading them to conclude that the perps most likely were able to take advantage of the machines simply by observing the the machine's behavior and taking advantage of patterns of play on the machines that the hackers were somehow able to track.

More in this incredible story here...
https://www.wired.com/2017/02/russians-engineer-brilliant-slot-machine-cheat-casinos-no-fix/