Hackers stole Social Security numbers and other personal data for about 21.5 million people in breaches of the U.S. government's personnel office, the Obama administration said.

The Office of Personnel Management, the government's human- resources agency, disclosed the results of an investigation into the hacks Thursday in a news release. The 21.5 million includes 19.7 million individuals who applied for a background investigation, and 1.8 million non-applicants, such as spouses of applicants. Personal information from U.S. job applicants who went through federal government background checks while applying for security clearances was breached in the intrusions, which OPM discovered in April. The FBI has been investigating since.

The new numbers vastly expand the publicly disclosed scope of the hack, which targeted federal government employees and contractors. The White House had previously said more than 4 million people may have had their data stolen. It later discovered a second breach targeting more than 21 million people who had gone through federal background checks.

"If an individual underwent a background investigation through OPM in 2000 or afterwards," OPM said in a release Thursday, "it is highly likely that the individual is impacted by this cyber breach."

Several government employees have expressed frustration in the wake of the hack, accusing OPM of withholding information about its scope and failing to provide adequate protections against identity theft.

Lawsuit Filed

U.S. Treasury employees filed suit this week seeking lifetime credit monitoring and calling the attack a violation of the constitutional right to privacy. The American Federation of Government Employees placed a full-page ad in Politico on Thursday, calling for OPM to release more information about the scope of the breach.

"AFGE remains frustrated by the lack of information being provided by OPM on the number of current, retired and prospective employees whose information was stolen," the labor union said Thursday in a statement. "OPM also has not detailed what information was stolen, leaving millions of employees anxiously waiting for answers."

The union, which has called for free lifetime credit monitoring for affected individuals, filed a class-action complaint against OPM last month.

OPM has offered credit monitoring and identity theft services to affected employees.