> I would introduce subtle errors into the data manipulated by the program I no longer remember the games, but in the 80s copy protected games, I remember some

> I would introduce subtle errors into the data manipulated by the program I no longer remember the games, but in the 80s copy protected games, I remember some where if the game detected it was a cracked copy it would still run fine but the game would be missing critical items so it became impossible to progress. Unless you knew this, you could go crazy trying to find the items that didn't exist.