"They're not random," A.J. says. "The first three digits have to do with where you're born. I was born in New York so I have 095; if you're born in California, you're in the 500s—it sort of goes from east to west. The middle two [digits] have to do with when you were born. And then the last four are totally random. … So if you know someone's social security number, you can basically figure out where they were born and how old they are."