I've got a post up today on the Popular Mechanics website with an interview I conducted yesterday with cryptology expert and security consultant Bruce Schneier, who since 9/11 has been one of the most pointed critics of the government's anti-terrorism security programs. In his 2003 book Beyond he coined the phrase "security theater" to refer to measures which are undertaken not because they will be effective at thwarting attacks, but because the agencies carrying them out need to appear to be doing something useful. I asked Schneier about the recent controversy involving the Transport Security Agency's use of invasive scanners and full-body pat-downs. You can read the full interview here. Here's the transcript:

What is really being seen by these machines?

In theory, it sees stuff that isn't part of the body. So if you've got a stapler in your pocket, it will show up. The thought is that it will see stuff that a metal detector won't detect, like a ceramic knife. But this doesn't seem to be borne out by reality.

The machines have shown up in the wake of the so-called underwear bomber, who tried to blow up a plane with chemicals stored in his briefs. Would this technology have stopped him?

The guys who make the machines have said, "We wouldn't have caught that."

So what kind of attack will this prevent, that otherwise might be successful?

There are two kinds of hijackers. There's the lone nutcase, like someone who will bring a gun onto a plane because, dammit, they're going to take the whole plane down with them. Any pre-9-11 airport would catch a person like that. The second kind is the well-planned, well-financed Al Qaeda-like plot. And nothing can be done to stop someone like that.

Has there been a case since 9/11 of an attempted hijacker being thwarted by airport security?

None that we've heard of. The TSA will say, "Oh, we're not allowed to talk about successes." That's actually bullsh*t. They talk about successes all the time. If they did catch someone, especially during the Bush years, you could be damned sure we'd know about it. And the fact that we didn't means that there weren't any. Because the threat was imaginary. It's not much of a threat. As excess deaths go, it's just way down in the noise. More than 40,000 people die each year in car crashes. It's 9/11 every month. The threat is really overblown.

Do you think there's been an over-reaction, on the part of the government and the press, to the underwear bomber?

That case was really instructive. Nobody was injured, and the plane landed safely. It was a success! And it was pre 9-11 security that made it a success. Because we screen for superficial guns and bombs, he had to resort to a syringe and 90 minutes in the bathroom with a bomb that didn't work. This is what success looks like. Stop bellyaching!

What's the motive behind introducing this new level of security?

It's . You have to be seen as doing something, even if nothing is the smart thing to do. You can't be seen as doing nothing.

Does it surprise you that at last, after several escalations in the TSA's level of intrusiveness, the public seems to have finally rebelled?

Back in 2005, when this full-body scanner technology was first being proposed, I wrote that I thought this would be the straw that broke the camel's back, because it would unite conservatives and liberals. Nobody wants their daughter groped or shown naked.

Is privacy being violated, in your estimation?

You go get groped and you tell me.

Have you had a pat-down?

Yes, actually, just a couple of days ago.

Is this security theater?

100 percent. It won't catch anybody.