The password for US nuclear silos was eight zeros for twenty years.
Why it is true
To ensure rapid launch, the code for all bases was set to 00000000 from 1962 until the mid-eighties, against the wishes of politicians.
Source: Smithsonian
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.