-- U.S. authorities became convinced that security measures for certain U.S.-bound flights needed to be boosted only after conducting a series of tests to determine the credibility of new intelligence, ABC News has learned.
Earlier this year, authorities obtained intelligence indicating that ISIS associates were trying to develop explosives-laden electronics that could be smuggled aboard planes, according to sources familiar with the intelligence.
The subsequent tests were executed in recent weeks, looking to determine whether terrorists could carry out the latest form of attack with a bomb hidden in electronics.
The tests led authorities to one conclusion: "It can be done," one source told ABC News.
Sources said that the airports affected by the restrictions were not directly named in the most recent threat intelligence gathered by authorities, but those airports were identified through intelligence analysis paired with other government information.
In an interview with ABC News, Rep. Eric Swalwell, D-Calif., a member of the House Intelligence Committee, warned about the "new aviation threat."
Nearly two years ago, ABC News first reported that an internal investigation of the Transportation Security Administration revealed security failures at dozens of major U.S. airports. Undercover investigators were able to smuggle mock explosives or banned weapons through checkpoints in 95 percent of trials. The series of tests were conducted by Homeland Security Red Teams who posed as passengers.