Dick Jacobs, 76 stands in a full-body scanner as he passes though an airport security check with his shoes and jacket on at Portland International Airport (PDX) March 19, 2012 in Portland, Oregon. (Natalie Behring/GETTY IMAGES)

One of the Transportation Security Administration’s vaunted 20 layers of security has been looking a little porous lately, and the resulting dust-up is calling into question the effectiveness — and the cost-effectiveness — of post-9/11 airport screening.

I’m talking, of course, about the TSA’s controversial full-body scanners, also known as advanced imaging technology.

Depending on whom you believe, a 27-year-old engineer named Jonathan Corbett this month either exposed the scanners as seriously defectiveor pointed out a minor flaw that insiders had known about for a while. Either way, his actions have raised serious concerns among air travelers, not the least of which is whether we’re less safe now that the bad guys know how to squeak past our shiny new scanners — if indeed they do.

A video clip posted online March 5 purportedly shows how Corbett outsmarted the scanners: He sewed a pocket to the side of a shirt, placed a metal carrying case that he says would “easily alarm any of the old metal detectors” inside it and walked through the two types of full-body scanners now in use, without incident. Corbett’s theory was that the case, hanging to the side of his body rather than in front of or behind it, would disappear into the black background of the scanned image, thus escaping detection. Even though claims of the scanners’ fallibility weren’t new, the video promptly went viral, capturing more than a million views within a few days.

Corbett says that the idea of discrediting the TSA scanners came to him after he read a report saying that the New York City Police Department is deploying similar technology to detect contraband from afar. He wondered whether he could invent something that would render the NYPD scanner useless.

“It didn’t take long to realize that I could apply that same entrepreneurship to the TSA’s nude body scanners and invent a holster that would make its contents invisible to the TSA,” he says.

The TSA quickly posted a response on its blog calling Corbett’s actions “a crude attempt to allegedly show how to circumvent TSA screening procedures.” But the agency didn’t dispute that Corbett had actually done that, leading many observers to conclude that he’d figured out how to thwart the $170,000 machines.

“That’s not a fair interpretation,” TSA spokesman Greg Soule says. “That said, for obvious security reasons, TSA can’t discuss our technology’s detection capabilities in detail.”

Here’s what the agency will say: The scanners are safe and effective, part of a “layered, risk-based approach to security through screening technologies and applying intelligence to our security measures in real time.”

Adds Soule, “Our nation’s aviation system is safer now with the deployment of 600 imaging technology units at 140 airports.”

But not all travelers are convinced. Amy Rubins, a wedding planner and frequent traveler based in Minneapolis, says that she thinks the TSA has been less than forthright in the past about how the scanners would be used and whether they’re indisputably safe. So she’s also skeptical about the agency’s latest assertion. “Mr. Corbett’s video provided simple proof that the scanners are ineffective and can easily be beaten,” she says.

Jonathan Yarmis, a technology consultant in New York, says that his industry benefits from openness and transparency, so when the TSA refuses to discuss its scanners beyond insisting that they’re safe and effective, he’s suspicious. “When people resort to the ‘trust me’ defense, I have the exact opposite reaction: You must have something to hide,” he says. “The only people TSA is fooling are those who don’t actually fly or those who don’t actually care.”

Another frequent traveler who knows a thing or two about scanning technology says that the Corbett video can be explained in one of two ways. “Either TSA knew about this loophole and decided to ignore it because they had already invested political capital in these machines and had to double down,” says Jeremy Thompson, a former airline manager who is now a chiropractor in Atlanta, “or they didn’t know about this loophole. And that shows that they actually don’t understand what they’re doing.”

Thompson believes it’s the latter. “It seems to me that TSA is constantly trying to justify its latest whiz-bang gadget,” he says.

The passengers with whom I spoke told me they didn’t think that the video has affected the safety of air travel. They also agree that the video gives lawmakers, who are under pressure to cut government spending, an opportunity to review the advanced imaging technology program. This particular layer of security will cost taxpayers $2.3 billion in extra staffing over the machines’ seven-year life spans, according to a Government Accountability Office report. The scanners will set them back an additional $289 million or so.

Corbett, who writes a blog called TSA Out of Our Pants!, says that the reaction to his video brings him closer to his goal of revamping the TSA’s screening procedures. This has been his mission since 2010, when he filed a lawsuit against the TSA, claiming that the scanners are unconstitutional. “I want to see the scanners and the pat-downs disappear from airports and to see effective, noninvasive tools replace them,” he says. “It remains to be seen what the TSA will do about the scanners, but I do think this was, at the least, an important step on the path to their removal.”

Yes, but did this video just make air travel a little more dangerous?

That might be the wrong question, because it implies that full-body scanners have made us safer. But there’s no conclusive proof that advanced imaging technology is effective or, for that matter, safe.

Maybe Corbett’s video really established only one thing: that the TSA’s unproven screening technology remains exactly that — unproven.

Elliott is National Geographic Traveler magazine’s reader advocate and the author of “Scammed: How to Save Your Money and Find Better Service in a World of Schemes, Swindles, and Shady Deals.” E-mail him at chris@elliott.org.