(Bloomberg) -- Hackers in China breached U.S. Office ofPersonnel Management computers and stole personal records of asmany as 4 million current and former federal employees, a U.S.official said.

The hackers, believed to have links to the Chinese government,got into the government computer system last September, accordingto the official, who asked for anonymity to discuss theinvestigation.

A U.S. intelligence official said, also speaking on condition ofanonymity, Chinese hackers appear to have mounted an effort to getpersonnel files, health-care records and other personal informationon millions of government employees and contractors.

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The data could be used to target individuals with access tosensitive information who have financial, marital or other problemsand might be subject to bribery, blackmail, entrapment and othertraditional espionage tools, the official said.

The Federal Bureau of Investigation and the Department ofHomeland Security are investigating the hack, which was detected inApril, according to a statement from OPM.

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The federal government plans to notify those who werepotentially affected by the breach, and is offering free creditreport access, credit monitoring and identity-theft insurance andrecovery services to those whose personal information wascompromised.

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