When people see those shiny slot machines, the thought that instantly comes in their mind is about making these machines work like ATM machines. Enthusiastic players from all eras have tried to work out the secret patterns underlying the functioning of the machines and gain huge rewards. Most have failed, but a few have succeeded. 

Let's just look at the example of one most popular people to pull this trick off. This man was Ronald Harris. He always wanted to make a fool out of the slot machines and thus he kept working on formulas which would tell when a particular machine will give a payout. Slot machines work on the basis on RNG, which stands for Random Number Generator which keeps generating random numbers all round the clock. If a number which is preset in a machine as the winning number is generated and at the same time, a player pulls the handle, the Jackpot is activated.

As the random numbers are generated by algorithms, Ronald Harris worked on several machines to work out the algorithms used by them. He used a computer program for this purpose and thus calculated the exact time when the handle had to be pulled. Not only did he win many jackpots, but also he was caught, fined and banned from playing in casinos soon after his discovery.

However, Harris's achievement shows that Slot machines can be hacked on the condition that a person has access to the Random Numbers being generated by the machines. And obviously, after the disclosure of Harris's acts, the RNG display has been removed from machines and all access to it has been securely hidden.