Chinese hackers have reportedly broken into the Office of Personnel Management (OPM) to gain access to the personnel records of all US government employees who had applied for government security clearances.
There was no loss of personally identifiable information, said the Department of Homeland Security that had detected the breach.
The security of OPM is not as tight as the Pentagon's since it is a civilian agency, reports the Verge.
The government through Electronic Questionnaires for Investigations Processing (e-QIP), an electronic system that collects data on employees applying for such clearances, investigates employee backgrounds before giving clearances.
It is not clear whether an independent group had conducted the breach or Chinese government even though the hack was successfully traced.
Secretary of State John Kerry said after a meeting with Chinese officials that cyber security had been broadly discussed at the meeting.
A Chinese spokesperson said that China would always resist hacking and that such reports could not be refuted.