Washington, Jun 4 (EFE).– The personal data of up to four million U.S. federal employees may have been compromised by a massive cyberattack, which could have been the work of Chinese hackers, U.S. authorities said Thursday.

The hack-attacks occurred last December but were not detected until April, the U.S. government’s Office of Personnel Management said Thursday in a communique, adding that it is working with the FBI to investigate the data breach.

The OPM will sent notices to approximately four million people whose information could have been compromised, said the agency, which is the human resources department for the federal government, conducting more than 90 percent of federal background and security-clearance investigations.

U.S. officials told The Washington Post that they suspect the attacks were mounted by Chinese info-pirates.

The cyberattack could be the largest theft of federally-archived personnel data ever perpetrated against the United States. EFE