[mywittyname]

Doesn't the birthday paradox/pigeonhole principle apply here? If we assume that there are 1,000,000,000 unique values, then the square root of a billion (31,622) is all you need for a 50% chance of collision.

[smudgymcscmudge]

That's only if SSNs are randomly assigned. They aren't.

The issue is people are giving AT&T incorrect SSNs.

[selectodude]

Post-2011 they started making them random.