Chinese hackers are suspected of carrying out a “massive breach” affecting the personal data of millions of US government workers, officials said.
The Office of Personnel Management (OPM) confirmed on Thursday that almost four million current and past employees have been affected.
The breach could potentially affect every federal agency, officials said.
Using a new cyber security system known as Einstein, the OPM detected a “cyber-intrusion” in April 2015. The FBI said it was investigating the breach.
Ken Ammon, chief strategy officer of Xceedium – a cyber security firm – warned that the hacked data could be used to impersonate or blackmail federal employees with access to sensitive information.