From the Washington Post:
Since the Sept. 11, 2001, attacks, the Social Security Administration's vast databases of personal information have become a resource for federal investigators, who have asked the agency to check tens of thousands of records for number misuse and identity fraud -- potential precursors to terrorist activity. ...
The Social Security Administration is "the Fort Knox of identity information in the United States," said James Huse, the agency's inspector general from 1998 to 2004. "That's a pretty impressive investigative tool that no other agency possesses."
From just after Sept. 11 through 2005, Social Security officials sent prosecutors 456 referrals that were classified as terrorism-related, according to statistics compiled by Syracuse University's Transactional Records Access Clearinghouse. The review shows that 91 percent of those referrals led to prosecutions. ...
Still, few if any suspects in Social Security cases are ever linked publicly to alleged terrorist activity. Most cases referred to prosecutors in the months after Sept. 11 involved document fraud by Latino immigrants working at airports.