(Damian Dovarganes/Associated Press)

The government is notifying journalists who are accredited by federal agencies that their personal information may have been stolen by the Chinese, another sign of the breadth of the massive hack of U.S. computer networks.

The exposure of Social Security numbers and other personal data of people who never worked for the government, but have or once may have had access to federal buildings, could involve hundreds and as many as thousands of reporters, photographers and cameramen and women who regularly cover the White House and hundreds of agencies in Washington and nationwide.

Reporters who write about the Defense Department, the White House and the CIA for The Washington Post confirmed that they have received letters in recent weeks, telling them their personal information may have been stolen and urging them to sign up for free credit monitoring and identity-theft protection.

[Final notices out this week for victims of the Chinese hack]

The Office of Personnel Management sent final notices last week to more than 21 million current and former federal employees and contractors to inform them that the background investigation files used to vet them for security clearances were exposed by the hackers, who U.S. officials have privately said were with the Chinese government. The breach involved people who applied for security clearances or had them renewed since about 2000 and in some cases earlier.

OPM officials said when they disclosed the intrusion months ago that the stolen data was limited to federal employees and contractors with Social Security numbers, performance evaluations, and, in some cases, family members and friends who were listed as references on millions of applications for security clearances.

[Facing uproar over its handling of hack, contractor responds, ‘We took a beating for doing what was right."]

But background investigations, it turns out, are not done only on federal employees or contractors applying for clearances because they handle sensitive or classified information or are in what are called positions of trust.

Journalists, contractors without access to sensitive material, and even volunteers who go in and out of federal buildings also are thoroughly vetted, albeit through a less rigorous process, as long as they want credentials for regular access to a facility for a period of at least six months.

“Many of the background investigations that OPM conducts are for suitability for federal employment and security, not just for a security clearance,” spokesman Sam Schumach said in an email. “Many individuals, including reporters who need long-term access to federal buildings, may undergo a routine background check in order to obtain valid credentials.”

[What to do if you’re a federal worker and your information was stolen]

The vetting of journalists, in other words, is similar to what’s done for much of the federal workforce. They’re not high-level background investigations like a CIA officer, diplomat or someone handling nuclear materials would go through, but the government still wants to know if the person has a criminal history, if they are who they say they are and whether their work history checks out. A fingerprint check usually is involved, and the person submits a Social Security number, date of birth, address and a few other details of their identity.

The requirement for those seeking regular access to federal buildings followed a Homeland Security directive issued after the terrorist attacks of Sept. 11, 2001.

[Reacting to Chinese hack, the government may not have followed its own cybersecurity rules]

“We do background investigations for many agencies for this purpose,” said a senior OPM official who is familiar with the process. “It’s entirely possible that those journalists who have a Social Security number in the system were in this group.”

OPM does hundreds of thousands of background checks on this level every year, the official said.