COMPROMISED : Chinese Hackers Hit Nearly Every Agency... 4 Million Identities Exposed...Could Be The Biggest Cyberattack In U.S. History...Third Major Breach This Year... FBI Investigating... China: U.S. Comments Irresponsible...

AP  |  By KEN DILANIAN and RICARDO ALONSO-ZALDIVAR Posted: 06/04/2015 5:19 pm EDT 

US and Chinese Flags

WASHINGTON (AP) — China-based hackers are suspected of breaking into the computer networks of the U.S. government personnel office and stealing identifying information of at least 4 million federal workers, American officials said Thursday.

The Department of Homeland Security said in a statement that data from the Office of Personnel Management and the Interior Department had been compromised. "The FBI is conducting an investigation to identify how and why this occurred," the statement said. The hackers were believed to be based in China, said Sen. Susan Collins, a Maine Republican.

President Obama

Collins, a member of the Senate intelligence committee, said the breach was "yet another indication of a foreign power probing successfully and focusing on what appears to be data that would identify people with security clearances."

A spokesman for the Chinese Embassy in Washington called such accusations "not responsible and counterproductive."

"Cyberattacks conducted across countries are hard to track and therefore the source of attacks is difficult to identify," spokesman Zhu Haiquan said Thursday night. He added that hacking can "only be addressed by international cooperation based on mutual trust and mutual respect." more