On July 9, 2015, the Office of Personnel Management announced that deeply personal data for 21.5 million federal employees, contractors, applicants, and family members was stolen in a breach of security clearance information.
This sensitive data included, but was not limited to: "identification details such as Social Security Numbers (SSN); residency and educational history; employment history; information about immediate family and other personal and business acquaintances; health, criminal and financial history; findings from interviews conducted by background investigators, and fingerprints."
The act of issuing new SSN to all impacted personnel would make it more difficult for identity thieves to effectively use the compromised data, potentially protecting millions from fraud.