Short Answer


Longer Answer

Rion Williams has a good blog post with an explanation of the rules.

In a nutshell, social security numbers must not do any of the following:

  • Start with 000, 666, or 9
  • Have 00 as the middle two digits
  • Have 0000 as the last four digits
  • Cannot be 078-05-1120 because of the Woolworth card
  • Cannot be 219-09-9999 as that appeared in an ad by the SSN administration

The regular expression above validates for all of these conditions, with dashes included.