Since current airport security technology is largely reactive to known threats, competent evil doers will eventually change their tactics to skirt by and do their worst. With that in mind, a new tactic could be pancakes.
Not pancakes you'd necessarily eat, of course, but PETN pancakes. Potential attackers would take the notoriously explosive material and smooth it into a pancake shape to mimic the contours of the abdomen using dimensions of about about 15-20cm in diameter and 1cm thick. Voila, hidden explosive.
This, according to a report in the Journal of Transportation Security (emphasis mine):
It is very likely that a large (15-20 cm in diameter), irregularly-shaped, cm-thick pancake with beveled edges, taped to the abdomen, would be invisible to this technology, ironically, because of its large volume, since it is easily confused with normal anatomy. Thus, a third of a kilo of PETN, easily picked up in a competent pat down, would be missed by backscatter "high technology". Forty grams of PETN, a purportedly dangerous amount, would fit in a 1.25 mm-thick pancake of the dimensions simulated here and be virtually invisible. Packed in a compact mode, say, a 1 cm×4 cm×5 cm brick, it would be detected.
Where a simple pat down would effectively mitigate this threat (Cost: TSA worker's salary), the multi-million dollar nudie machines would do nothing.
Oh, and conspicuous wires and thin blades? Potentially invisible as well:
The images are very sensitive to the presence of large pieces of high Z material, e. g., iron, but unless the spatial resolution is good, thin wires will be missed because of partial volume effects. It is also easy to see that an object such as a wire or a box- cutter blade, taped to the side of the body, or even a small gun in the same location, will be invisible. While there are technical means to mildly increase the conspicuity of a thick object in air, they are ineffective for thin objects such as blades when they are aligned close to the beam direction.
I guess I've never had too much of an issue being scanned, so it's not even a privacy issue anymore, with me. It's just the incredible waste of money on an ineffective technology that really bothers me (more than any curious gloved TSA hand ever could, anyway). I would say the same of a professional football team that bought the latest and greatest hockey sticks for their linemen. [Journal of Transportation Security (PDF) via Boing Boinghttp://www.boingboing.net/2010/12/11/pornoscanners-trivia.html]