Want to get on an airplane? Let's see your scrotum.

Another privacy advocate tells the Times: "If there are a hundred tactics and I protect against two of them, I'm not making you safer. If we use full-body scanning, they're going to do something else."

Wrong again. It's true that if we use the scanners, bombers will change tactics. But that isn't failure. It's success. Security is a constant arms race against innovative malefactors. By pursuing them in Afghanistan and Pakistan, you force them to Yemen. By tracking their cell phones, you force them to use couriers. By hunting them with drones in the mountains, you force them into cities. You can't stop them, but you can cripple them and keep them off balance.

Scanners can detect bomb powder sewn into underwear. The terrorists' logical next step is to put the powder where the scanners can't find it: inside their bodies. That may be what the Saudi bomber did. But look at the resulting complications. It's a lot harder to reach a bomb in your rectum than in your underwear. Perhaps that's why the Saudi bomber, according to CBS News, needed a cell phone to detonate his powder. And he failed to kill his target even though he was standing right next to him when the bomb went off. The bomber's body may have smothered the blast.

In a May 31 letter to Homeland Security Secretary Janet Napolitano, 34 privacy groups raise a further objection to the scanners: After repeatedly assuring the public that the scanners would be used only on passengers selected for secondary screening, TSA has begun to use them on all passengers at some airports. Why should we trust any other assurances from the government?

I agree. In April, I made the same point in Slate: TSA's track record shows it will do whatever it thinks it needs to do, regardless of prior assurances. Any detail omitted by airport screeners—a blurred crotch in the body scan, an untouched groin during the pat-down—will become a loophole exploited by terrorists. These loopholes, in turn, will have to be closed.

I still believe that. But the Detroit bomb has changed the equation. The blurred crotch is no longer an abstract problem. It's a demonstrated threat, with hundreds of lives at stake.

Let go of your fear of nudity. In the age of pubic powdered explosives, we can't let you board a plane without somebody scrutinizing your naked body. But we can offer you a different kind of privacy: Nobody who sees your naked body will see your face. That's how the TSA system works: The naked image shows up in a separate room without facial detail. The officer who sees you in the flesh never sees you on the monitor. The officer who sees you on the monitor never sees you in the flesh. It's like the blind men and the elephant: Nobody has the whole picture.

To its credit, TSA has become more explicit about the technology. In April, I complained that the agency had removed a frontal scan of a male passenger from its Web site and had limited its posted images to four scans so tiny you'd need a magnifying glass to see them. Guess what? TSA has now posted a magnifying glass so you can examine the resulting crotch scans in all their glory. Each guy's cleft and scrotum are so clear you can see exactly what's tucked where. That kind of transparency used to scare me. Now it's a relief.

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