Democratic presidential nominee Hillary Clinton’s sending of U.S. intelligence information to her campaign chair’s unsecured email address is “unquestionably” an operations security violation, according to an intelligence expert.

“It’s unquestionably an OPSEC violation,” Dr. John Schindler, a former NSA analyst and national security expert, told The Daily Caller News Foundation, regarding an email Clinton sent to Podesta that included U.S. intelligence sources.

OPSEC stands for operations security — meaning the keeping of critical military intelligence out of enemy hands. The email was published online by WikiLeaks from Clinton aide John Podesta’s hacked Gmail account.

U.S. intelligence officials suspect Russia was behind the hack, and a private cyber security firm recently linked the hackers were linked Russian intelligence.

Schindler said specific information in the hacked email regarding a confidential “source in Tripoli” was “not something anybody should be putting in unclassified email.”

Clinton sent Podesta an email in August 2014 giving her assessment of what needs to be done in the Middle East. Clinton said her sources were based on “Western intelligence, US intelligence and sources” in the Middle East, and specifically referred to a source in Libya.

[dcquiz] “A source in Tripoli stated in confidence that when the U.S. Embassy was evacuated, the presence of two U.S. Navy jet fighters over the city brought all fighting to a halt for several hours, as Islamist forces were not certain that these aircraft would not also provide close ground support for moderate government forces,” Clinton wrote to Podesta.

The email was one of thousands of published online by WikiLeaks. Schindler said it’s unclear if the email contained any “secret” information or what classification of the intelligence was Clinton presented to Podesta.

“It’s tough to say if it’s secret — US military moves usually are considered such at the time it happens,” Schindler said, adding the “exact classification would depend on how they learned this.”

Clinton sent the email from a private account she began using after leaving the Department of State that’s based out of her home in Chappaqua, New York. The FBI has already investigated Clinton over her handling of classified information while serving as Secretary of State, including storing classified materials on her private email server.

FBI Director James Comey said Clinton’s handling of classified materials was “extremely careless,” but declined to recommend bringing charges against the former State Department head.

Saagar Enjeti contributed to this report.

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