IN PHOTO: The U.S. Office of Personnel Management building in Washington June 5, 2015. In the latest in a string of intrusions into U.S. agencies' high-tech systems, the Office of Personnel Management (OPM) suffered what appeared to be one of the largest breaches of information ever on government workers.

IN PHOTO: The U.S. Office of Personnel Management building in Washington June 5, 2015. In the latest in a string of intrusions into U.S. agencies' high-tech systems, the Office of Personnel Management (OPM) suffered what appeared to be one of the largest breaches of information ever on government workers. REUTERS/Gary Cameron

U.S. administration officials said hackers may have compromised sensitive information, such as applications for security clearances of the government employees. The disclosure came a week after officials confirmed almost four million federal employees’ information was hacked. The officials blamed the attack on the Chinese.

According to CNN, clearances higher than top secret might not have been compromised. But some employees with lower-level access might had placed some personal information unintentionally.

"During the investigation into the cyber-intrusion of OPM that compromised personnel records of current and former federal employees announced last week, investigators became aware of an additional intrusion affecting different OPM systems and data," a senior administration told CNN on Friday.

Following this confirmation, the federal personnel chief, J. David Cox, sent a letter to Office of Personnel director Katherine Archuleta. The letter said union believes 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.”

He added the hackers also stole a range of personal information including military records, veterans’ status and life insurance information. The American Federation For Government Employees said the Central Personnel Data File is the main target of the hackers.

Cox mentioned the Social Security numbers were not encrypted, leading the cybersecurity to fail. On Thursday, National Journal reports the Senate rejected a push by Majority leader Mitch McConnell, which is about allow a cybersecurity measure to be added as amendment in an ongoing debate over National Defense Authorization Act.

Based on Washington Post report, the database became part of another database called Enterprise Human Resources Integration, which is managed by a business centre at the department of Interior several years ago. The database most likely contains the personnel files.

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