Advisers Chris Christie and Retired Army Lt. Michael Flynn accompanied Trump to the briefing.
Donald Trump has received his first classified briefing by the Office of the Director of National Intelligence on Wednesday.
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Former CIA agent David Priess, author of The President’s Book of Secrets, told Inside Edition Trump was brought up to speed on “things like ISIS, the situation in Syria, the threat from China. So the issues are serious."
He added: “They can be very informative on a whole range of policy issues, but do not give away the inner workings of the U.S. government's operations overseas.”
Two of Trump's top advisors, New Jersey Governor Chris Christie and retired Army Lieutenant General Michael Flynn — who spoke at the Republican Convention last month — accompanied him to the meeting in New York at a secure FBI facility.
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The contentious presidential campaign has led to reservations by some about whether Trump or Hillary Clinton can be trusted with classified information.
Priess said: "You have two unusual candidates. The two least popular candidates in history, both of whom have a potential concern regarding these briefings."
Briefings with presidential candidates have been conducted since the 1950s.
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