Peter this is fishy question.... however to satisfy your curiosity
- They use a trick in computer science called Uniform Random Distribution. The concept assumes that if you pick a billion numbers and randomly pick 100,000 or so unique numbers then the probability that someone will guess is almost impossible.
- They never use pure random numbers (which is impossible to generate anyway) but use uniform random which means that I can not get the same numbers as the previous numbers. As the space gets depleted they move to next billion space. This goes on and so forth etc
Becasue of depletion of space, that is why your card must be used within a certain period.
regards,
Paul.
--
"Change is slow and gradual. It requires hardwork, a bit of
luck, a fair amount of self-sacrifice and a lot of patience."
Roy.