AP Photo/ Louis Lanzano Agents from the FBI and other law enforcement agencies work at a 24-hour operations center at FBI headquarters, Monday, May 3, 2010, in the Chelsea section of New York. The center was set up to coordinate the investigation of the Times Square incident involving a vehicle loaded with explosive material.
Some FBI employees were notified in May that their files had been accessed by hackers during the massive, year-long breach of OPM's database, an FBI source told Newsweek.
More than 36,000 people work for the FBI, and while it remains unclear how many were affected, access to any FBI personnel files could have "mind boggling" effects, the same source said, "because there are counterintelligence implications, national security implications."
The hackers' alleged theft of military and intelligence officials' SF86 forms from OPM could be used to blackmail, exploit, or recruit US intelligence officers.
The 120-page SF86 form is an exhaustive examination of the life of anyone applying for government security clearance, including financial records (with gambling addictions and any outstanding debt), drug use, alcoholism, arrests, psychological and emotional health, foreign travel, foreign contacts, and an extensive list of all relatives.
As members of the intelligence community, FBI employees' forms were stolen, too.
As a result, spies who took OPM information will know "who the best targets for espionage are in the United States," Michael Adams, a computer security expert with more than two decades' experience in the U.S. Special Operations Command, told The Daily Beast.
"This is the most successful cyber attack in the history of the United States," he added.
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The Theodore Roosevelt Federal Building that houses the Office of Personnel Management headquarters is shown June 5, 2015 in Washington, DC. U.S. investigators have said that at least four million current and former federal employees might have had their personal information stolen by Chinese hackers.
Hackers who infiltrated OPM had access to the agency's security clearance computer system for over a year, the Washington Post reported, giving them ample time to steal as much information as possible from OPM's database of military and intelligence officials.
Joel Brenner, who from 2006 to 2009 served as the Intelligence Community's top counterintelligence official, described the hack to AP as "crown jewels material, a goldmine" for China, adding: "This is not the end of American human intelligence, but it's a significant blow."
"I'm really glad to be out of the game," a recently retired CIA senior operations officer told former NSA intelligence analyst John Schindler in a Daily Beast article.
"There's bad, there's worse - and there's this," The former CIA officer said, referring to the breach. "CIA officers are not supposed to be anywhere in OPM files, but I'm glad I'm not posted overseas right now, hoping that's true."