US government agencies have been hit by a "massive breach" affecting the personal data of millions of federal workers, officials say.
The Office of Personnel Management (OPM) confirmed on Thursday that almost four million current and past employees had been affected.
The agency serves as the human resource department for the federal government.
US government agencies have been hit by a "massive breach. Photo: Wikicommons
US officials suspect that the cyber attack originated in China.
The OPM issues security clearances and compiles records of all federal government employees.
Senator Susan Collins, a member of the Senate Intelligence Committee called the breach "yet another indication of a foreign power probing successfully and focusing on what appears to be data that would identify people with security clearances."
Using a new cyber security system known as Einstein, the OPM detected a "cyber-intrusion" in April 2015. The FBI said it is investigating the breach.
Congressman Adam Schiff has called for cyber databases to be upgraded in light of the most recent attack.
Americans "expect that federal computer networks are maintained with state of the art defences", Mr Schiff said.
"The cyber threat from hackers, criminals, terrorists and state actors is one of the greatest challenges we face on a daily bases, and it's clear that a substantial improvement in our cyber databases and defences is perilously overdue."
Marie Harf, a spokeswoman for the State Department, would not confirm that the Chinese government was behind the hack.
"There are a number of actors around the world who have these kinds of capabilities, and unfortunately that number continues to grow," Ms Harf told CNN.
- BBC
