A new report from Fox News shows that the entire U.S. national security system was likely undermined by a year-long hacking attack that was spotlighted by the revelations of 21.5 million Americans having their data stolen from the Office of Personnel Management (OPM).

Experts who spoke with Fox say that the data taken is so sensitive that it could be used to blackmail leaders or those who could be elected to public office in the future.

“There may be people walking around with higher levels of clearance than they should have,” one expert told Fox. “I believe the entire national security apparatus is now at risk. It’s mind-boggling.”

“It’s the digital equivalent of Pearl Harbor,” another expert added. “Because people don’t see the carnage, they don’t recognize that this is the equivalent of an act of war. This is about espionage—Cold War tactics in the modern digital age.”

Also being revealed is that contractors to OPM that conducted background checks were hacked.  A firm named USIS who worked for Homeland Security was hacked in December 2014; Keypoint, who took over the USIS contract, was hacked in June 2015.

Director of National Intelligence James Clapper has said that China is the leading suspect behind the massive, year-long hacking attack.

The report comes a day after OPM said they are working with the Defense Department to notify anyone impacted by the attack and provide them with identify-fraud protection services.  The contractor for the project will likely not be chosen until mid-August.

OPM plans to provide the free monitoring for those victimized by the hack for three years.