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.

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 Senator Susan Collins, a Maine Republican.

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

A US official, who declined to be named because he was not authorised to publicly discuss the data breach, said it could potentially affect every federal agency. One key question is whether intelligence agency employee information was stolen.

“This is an attack against the nation,” said Ken Ammon, chief strategy officer of Xceedium, who said the attack fit the pattern of those carried out by nation states for the purpose of espionage. The information stolen could be used to impersonate or blackmail federal employees with access to sensitive information, he said.

The Office of Personnel Management is the human resources department for the federal government, and it conducts background checks for security clearances. The OPM conducts more than 90 percent of federal background investigations, according to its website.

In November, a former DHS contractor disclosed another cyberbreach that compromised the private files of more than 25,000 DHS workers and thousands of other federal employees.

Cyber-security experts also noted that the OPM was targeted a year ago in a cyber-attack that was suspected of originating in China. In that case, authorities reported no personal information was stolen.

One expert said it’s possible that hackers could use information from government personnel files for financial gain.

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