From what I understand, they're supposed to be unique, but there are millions of cases where one person has more than one SSN, the same SSN is accidentally or i

From what I understand, they're supposed to be unique, but there are millions of cases where one person has more than one SSN, the same SSN is accidentally or intentionally used by multiple people, etc. http://www.computerworld.com/article/2552992/it-management/not-so-unique.html http://www.computerworld.com/article/2552992/it-management/n... There are also plenty of people who just plain don't have social security numbers, like the Old Order Amish.