Excerpted from: http://waysandmeans.house.gov/hearings.asp?formmode=printfriendly&id=4708
"To further increase the ease and convenience of verifying employee SSNs, SSA developed the Social Security Number Verification Service (SSNVS), which is an internet option that permits employer’s to quickly verify the accuracy of employees’ names and SSNs by matching the employee-provided information with SSA’s records. SSA expanded this service to all employers in June 2005. We processed over 25.7 million verifications for over 12,000 employers in 2005. "
"The information the employer submits to DHS is sent to SSA to verify that the social security number and name submitted match information in SSA records. SSA will also confirm US citizenship, thereby confirming work authorization; DHS confirms current work authorization for all non-citizens. DHS will notify the employer of the employee’s current work authorization status. This program is also available to all employers, subject to available resources."
And how is one to verify somebody with a stolen SS card who uses the stolen name as well?