 -- An internal investigation of the Transportation Security Administration revealed security failures at dozens of the nation’s busiest airports, where undercover investigators were able to smuggle mock explosives or banned weapons through checkpoints in 95 percent of trials, ABC News has learned.

The series of tests were conducted by Homeland Security Red Teams who pose as passengers, setting out to beat the system.

According to officials briefed on the results of a recent Homeland Security Inspector General’s report, TSA agents failed 67 out of 70 tests, with Red Team members repeatedly able to get potential weapons through checkpoints.

In one test an undercover agent was stopped after setting off an alarm at a magnetometer, but TSA screeners failed to detect a fake explosive device that was taped to his back during a follow-on pat down.

Officials would not divulge the exact time period of the testing other than to say it concluded recently.

Homeland Security Secretary Jeh Johnson was apparently so frustrated by the findings he sought a detailed briefing on them last week at TSA headquarters in Arlington, Virginia, according to sources. U.S. officials insisted changes have already been made at airports to address vulnerabilities identified by the latest tests.

“Upon learning the initial findings of the Office of Inspector General's report, Secretary Johnson immediately directed TSA to implement a series of actions, several of which are now in place, to address the issues raised in the report,” the DHS said in a written statement to ABC News.

Homeland security officials insist that security at the nation’s airports is strong – that there are layers of security including bomb sniffing dogs and other technologies seen and unseen. But the officials that ABC News spoke to admit these were disappointing results.

This is not the first time the TSA has had trouble spotting Red Team agents. A similar episode played out in 2013, when an undercover investigator with a fake bomb hidden on his body passed through a metal detector, went through a pat-down at New Jersey's Newark Liberty Airport, and was never caught.

At the time, the TSA said Red Team tests occurred weekly all over the United States and were meant to “push the boundaries of our people, processes, and technology.”

“We know that the adversary innovates and we have to push ourselves to capacity in order to remain one step ahead,” a TSA official wrote on the agency’s blog in March 2013. “[O]ur testers often make these covert tests as difficult as possible.”

In a 2013 hearing on Capitol Hill, then-TSA administrator John Pistole, described the Red Team as “super terrorists,” who know precisely which weaknesses to exploit.

“[Testers] know exactly what our protocols are. They can create and devise and conceal items that … not even the best terrorists would be able to do,” Pistole told lawmakers at a House hearing.

More recently, the DHS inspector general’s office concluded a series of undercover tests targeting checked baggage screening at airports across the country.

That review found “vulnerabilities” throughout the system, attributing them to human error and technological failures, according to a three-paragraph summary of the review released in September.

In addition, the review determined that despite spending $540 million for checked baggage screening equipment and another $11 million for training since a previous review in 2009, the TSA failed to make any noticeable improvements in that time.

ABC News’ David Kerley contributed to this report.