The number of current and former federal employees who had their personal information hacked may be far higher than the Obama administration originally disclosed, The Associated Press said based on two unnamed sources who the newswire noted "were briefed on the investigation."

The White House acknowledges that up to 4 million workers were affected by a December cyber breach, though it did not detail what information was accessed on Office of Personnel Management (OPM) servers; but the unidentified officials told the AP that between 9 million and 14 million may have had their personnel data and Social Security numbers stolen.

The national president of the American Federation of Government Employees (AFGE), David Cox, meanwhile, concurred in a letter to the OPM director that the hack was much broader than previously thought, Fox News reported.

"Based on the sketchy information OPM has provided, we believe that the Central Personnel Data File was the targeted database, and that the hackers are now in possession of all personnel data for every federal employee, every federal retiree, and up to one million former federal employees," Cox claimed in the letter, which was dated Thursday.

The union leader accused the agency of failing to take the proper precautions to protect federal employees' sensitive data, nothing that OPM keeps up to 780 separate pieces of information on each person, Engadget noted. The Office of Personnel Management also doubles as a "repository for extremely sensitive information" that comes from background investigations of employees and contractors who apply for security clearances, the AP detailed.

"We believe that Social Security numbers were not encrypted, a cybersecurity failure that is absolutely indefensible and outrageous," Cox wrote. "Very little substantive information has been shared with us, despite the fact that we represent more than 670,000 federal employees in departments and agencies throughout the executive branch," he added.

The AFGE president said that other information stolen from the OPM database may include workers' age, gender and race details; addresses; dates of birth; employment and pay history; health insurance, life insurance and retirement data; and military records and veterans status.