I've posted elsewhere in this thread about this. There's really no reason to expect SSNs as strings for internal use. 32bit integers readily represent the same, as the max SSN is just a 9-digit number. I've seen at least one client store SSNs as INTs in a database and handle left-padding to 9 characters and interposing hyphens in display code.

Any 9-digit integers are immediately suspect under this reasonable storage choice.