Besides that, it's a horrible, horrible secret. Until just a few years ago the first five digits could be easily determined from your birthday and location of birth, leaving only 4 digits of somewhat randomness, and even that went in sequential order, giving you a pretty good guess at a much small range. To add insult to injury, whenever a company thinks they are helping you keep it secret they will ask you for the last four digits of the number, the only four digits that actually matter.