3 facts for ya!

[NervousTyler]

1. In the Atari port of Donkey kong , the programmer hid his name inside an easter egg, which was so well hidden, that it was discovered after 26 years. Apparently the player should have a hi-score involving the numbers 3-4-7 e.g 34700 e.t.c.

2. Mother 2 (or Earthbound) uses strong anti-piracy measures, involving 2 anti-piracy messages, a highly increased rate of encountering enemies and the capability of destoying all saved data at a certain point of the game. This occured through subroutines and checksums, well hidden inside the game code.

3. Using the Missingno glitch in Pokemon Yellow would trigger a bunch of your character's sprite marching all over the street, route, city or wherever you were.

EXTRA: In GTA IV, there is an anti-piracy measure, which makes the screen uncontrollably shaky, in order to frustate the illegal player.