📸

were permitted access to the system. It was breathtakingly easy, and left the VAX open to any hacker, no matter how untalented.

For SCICON staff the news was disastrous. To deliver their contract on time they would need to find the flaw in the standard VAX operating system and remedy it. At first they turned to Digital for help, but with time running out, SCICON's programmers began looking for a fix themselves, tearing apart the VAX operating system line by line. They were looking for a bug in the program that would prevent it from operating correctly,³ or an omission in the commands that would allow hackers simply to ignore the 'error' message.

To the SCICON team's surprise, they didn't find one. What they discovered instead was a piece of program code that appeared to have been deliberately added to the operating system to provide the secret entrance. To the SCICON researchers it looked like a deliberate 'back door'.

Back doors are often left in computer programs, usually to facilitate testing. Generally, they allow writers of things like computer games to jump quickly through the program without needing to play the game. For example, in the mid-1980s a game called Manic Miner involved manoeuvring a miner level by lever from the depths of the mine up to the surface, the game becoming progressively harder at each level. The programmer whose job it was to test the game needed a short cut between levels, so he introduced back doors that would take him directly to any one of his choosing. Inevitably, some players stumbled on to the hidden routes, which – ironically – increased the game's popularity.

Often back doors, or 'cheat modes', are deliberately built into games, encouraging the player to try to break the rules. Some computer magazines give tips on how to find the cheat modes; some games, like the popular 'Prince of Persia', are said to be impossible to win without resort to cheating. Back doors are also introduced for more mercenary reasons: legend has it that programmers include back doors on arcade games they create, and then supplement their incomes by playing the games at venues, like night clubs and casinos, that offer prizes.

Some arcade back doors are known. Occasionally, players stumble

📸