It is well known that people use stupid passwords on the internet. An alarming number use "Password" for every "secure" site they visit. The 1Password blog has an interesting post discussing the mathematics of a cartoon from xkcd.
But that is all by the way. Apparently until 1977 the launch code for American nuclear missiles was "00000000". That's a zero followed by seven other zeroes.
Naturally I remembered this scene from Spaceballs, where the villains are extorting the code to open the shield from King Roland: