Arcade games, operating in an unforgiving commercial environment, were pioneers in implementing anti-exploit systems to protect their revenue and ensure fair gameplay. Unlike modern online games, their defenses were primarily hardware-based and designed to be robust against physical tampering. The most common types of anti-exploit systems found in classic arcade cabinets include several key technologies.

One of the fundamental systems was the ROM Checksum verification. The game's code stored on ROM chips would include a calculated checksum value. Upon boot-up, the main CPU would perform a checksum calculation on the ROM data and compare it to the stored value. A mismatch would indicate that the ROM had been tampered with or replaced, typically causing the game to halt and display an error code, effectively preventing the use of pirated or modified game boards.

Another critical mechanism was the Watchdog Timer. This was a hardware circuit that required the game's software to send a "heartbeat" signal at regular intervals. If the game code crashed, entered an infinite loop, or was stopped by a cheat device, the heartbeat would cease. The watchdog timer, left unchecked, would automatically trigger a full system reset, disrupting any attempt to freeze the game state for analysis or manipulation.

Memory Protection was also a common tactic. Developers would implement checks to guard specific areas of memory. For instance, the routine that decremented the player's credit counter would verify that the operation was valid and that the memory address hadn't been altered by an external device. Writes to critical code areas or variables controlling lives and scores were often scrutinized to prevent unauthorized changes.

Furthermore, Tamper-Evident Hardware design served as a physical deterrent. Arcade cabinets were built with security screws and locks to prevent easy access to the printed circuit boards (PCBs). While not a digital system, this physical barrier was the first line of defense against individuals trying to attach cheat devices or modify the hardware directly.

Finally, some advanced systems employed Encryption and Scrambling. To combat reverse engineering, the data between the CPU and other chips (like graphic or sound processors) could be encrypted. The graphics data itself was sometimes stored in a scrambled format on the ROMs, making it meaningless without the proper descrambling algorithm hardwired into the custom graphics chip. This made creating bootleg copies of the game much more difficult.

Together, these systems formed a multi-layered defense strategy that was remarkably effective for its time, ensuring the integrity and profitability of arcade gaming.