The Office of the Inspector General (OIG) is the branch of SSA that investigates claims of fraud and prosecutes the offenders.
Some of their more interesting cases are reported in the Eye on OIG report that is published at the SSA website.
Here is an example of one of the latest cases:
In April 2005, a California man was sentenced in Honolulu, Hawaii to 60 months' incarceration in Federal prison, 3 years' probation, and restitution of $70,316 to SSA. He was also ordered to pay $237,407 to his ex-wife for unpaid child support. The conviction was based on an OI investigation that revealed the man assumed the identity of a deceased Title II disability beneficiary and convinced SSA that he was the individual entitled to the benefits and that the deceased beneficiary was an imposter.A subsequent investigation revealed that the man had fled the State of California and assumed the identity of the deceased beneficiary in order to avoid paying child support. In September 1995, the California Superior Court issued an arrest warrant for the man for failure to pay the child support. This case was referred by the SSA Honolulu Office. (Case Agent Chris Castellanos, Los Angeles Field Division)