Hillary Clinton’s home-brewed server held at least one email that contained highly sensitive information from human spying, according to a report Friday.
Fox News, citing two sources, reported that an intelligence agency identified the information as "HCS-O," the code used to report on human intelligence sources that are engaged in ongoing operations.
"The HSC-O compartment (Operations) is used to protect exceptionally fragile and unique IC [intelligence community] clandestine HUMINT operations and methods that are not intended for dissemination outside of the originating agency," a policy document released by the Office of the Director of National Intelligence in response to a Freedom of Information Act (FOIA) request explains.
"Personnel with access to HCS operational data must exercise deliberative caution in remarking legacy HCS to ensure it appropriately protects HCS-O information."
It is unclear whether the intelligence contained in the email revealed the identity of the human intelligence source.
The latest revelation follows a report earlier this week that the inspector general of the intelligence community penned a letter to top lawmakers revealing that an intelligence review identified "several dozen" classified Clinton emails, including some that contained intelligence from the government’s highly classified "special access programs."
Intelligence from special access programs is more sensitive than "top secret" information.
The letter, written by I. Charles McCullough III to lawmakers who oversee the intelligence community and the State Department, was also reported by Fox News.
A representative for Clinton’s presidential campaign dismissed the findings spelled out in McCullough’s letter, accusing the inspector general of coordinating with Republicans to damage the Democratic presidential candidate.
Clinton has maintained that she never sent nor received information marked classified on her personal email. The FBI has been investigating Clinton’s email setup since McCullough determined last summer that at least two emails held on her system contained top secret information at the time they were sent.