Security failures by the Transportation Security Administration allowed fake explosives and weapons through at dozens of the nation's busiest airports.

The internal tests were conducted by Homeland Security Red Teams, undercover investigators who pose as passengers with harmful objects hoping to get through TSA security checkpoints. According to a recently released Homeland Security Inspector General report, Red Team members were able to get through security checkpoints with potential weapons in 67 out of 70 tests.

"Upon learning the initial findings of the Office of Inspector General's report, [Homeland Security] Secretary [Jeh C.] 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," TSA told ABC News in a statement, though the statement did not identify the fixes.

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

The Red Team has exposed TSA issues before. In 2013, an agent made it through a metal detector with a fake bomb.

"[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," then TSA-administrator John Pistole told lawmakers at a 2013 Capitol Hill hearing about the Red Team.

This time around, U.S. officials insist changes have already been made to fix the weaknesses identified by the latest Homeland Security tests.