It was common practice in early Atari games to have custom, non-ASCII character sets. For Tempest, as an anti-tamper measure the team made the character assignm

It was common practice in early Atari games to have custom, non-ASCII character sets. For Tempest, as an anti-tamper measure the team made the character assignments for the game's copyright message executable 6502 code. Periodically, in an obfuscated way, the machine would execute this code. People who pirated the ROM (this did happen in the industry) would be tempted to modify the message; the machine would crash, and they'd have to figure it out. When the team (well, Dave Theurer) finished the game, they sent it off to the factory floor and went on vacation. Mission accomplished. Then Atari legal decided that they had to update the copyright message (e.g., to alter some spelling). Since the team was away, someone without the above knowledge just changed the string. The game appeared to work, and that's what they shipped. That modification didn't abjectly crash the machine. Instead, it did Weird Shit depending on the remainder of the score line. Just luck of the draw.