In the event of a slot machine malfunction, why would all winnings be invalid? "If the slot fails, all winnings are invalid". Why do online casinos impose such restrictions, and can they be used for a selfish purpose (not to pay the winner)? Let's try to solve this problem. What kinds of malfunctions can slot machines cause? The core of any slot is software. Moreover, what we see on the screen is: moving symbols, bonus games, winning combinations. This is a complete program account design. The calculations are based on RNG, which determines the gain or loss in a given number of spins. Computational calculations occur at even the smallest fraction of a second. The data received by the software is always compared and verified. Netent software is one of the most stable software in the casino industry.