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The bomb “was a threat from the standpoint of the design,” Mr. Brennan told ABC News. “And so now we’re trying to make sure that we take the measures that we need to prevent any other … similarly constructed [bomb] from getting through security procedures.”

Abdulmutallab’s underwear bomb was not spotted by metal detectors at Amsterdam’s Schipol airport.

After the failed attack, the Transportation Security Administration (TSA) sped up its deployment of advanced imaging technology screening devices, which have become notorious as the “naked X-ray” machines.

Analysts generally agree that the imaging machines should be able to spot the new underwear bomb, said Rep. Mike Rogers, Michigan Republican and chairman of the House Select Committee on Intelligence.

But in an interview with CNN, he cautioned that this was just a “preliminary conclusion. … We don’t know all of the facts yet.”

The key to imaging detection of underwear bombs is generally the detonator because it has to emerge from the clothing in which the explosives are concealed, said Erroll G. Southers, a homeland security scholar at the University of Southern California.

The TSA has deployed about 700 imaging machines at more than 180 U.S. airports, according to agency figures. The machines cost between $130,000 and $170,000 each, and the agency has spent nearly $167 million so far to buy, test, deliver and install them.

TSA has faced keen scrutiny of its efforts to roll out the machines and questions about the effectiveness of deploying them in the United States because all previous al Qaeda attacks against U.S. aviation have originated overseas.

“That is a huge gaping hole,” Mr. Southers said.

Inconsistencies in technology and policy from country to country undermine public confidence, he said, noting reports that the European Union this year will relax the no-liquids rule for air passengers’ hand luggage, which would put the European Union out of step with the U.S. The ban is designed to defeat another kind of nonmetallic explosive.

Investigators from the Government Accountability Office (GAO) will report at a congressional hearing Wednesday that TSA deployed the imaging technology at airports without evaluating it properly.

“Additionally, various reports, studies and independent testimony all suggest that TSA is ineffectively deploying security technology and equipment at commercial airports,” reads a staff memo for the hearing.