South Korean ID numbers are “master keys for hackers”

Wikipedia has lots of interesting info about South Korea's RRN number:

http://en.wikipedia.org/wiki/Resident_registration_number

Basically it's a 13-digit number with format yymmdd-sbbbbnc consisting of year, month, and day of birth, sex, birth location, a check digit, and single extra digit to differentiate persons who happen to have the same date and place of birth.

The US Social Security Number (SSN) encodes some personal info too, but not to this degree.

The nature of identity numbers--being permanent or very difficult to change--means that you can expect much confidentiality. But the South Korean design has eliminated all possibility of keeping it private. If you know a person fairly well, or they're a public figure, you can deduce the RRN. Conversely, if you get the RRN, you automatically get a lot of personal info.