机场安检机器故障 汗水误当爆炸物

National security officials are in high alert, we have more on that in a minute. But today we also learn there are new concerns about what we felt was one of the most sophisticated tools out there that keep terrorists off planes. Our chief investigate correspondent Brian Ross has been looking into this and he's got a lot more.

There are some 250 of the full body scan machines in question, being used at 40 airports across the country. Made by a US company, L-3 Communications, they use radio frequencies to scan for hidden weapons and explosives. At a cost of about 170,000 dollars each, US officials call them the best available technology. But that has now been challenged in Germany when officials announced this week the machines and the software are currently too unreliable to be used. A 10-month trial at the Hamburg airport found false alarms 49% of the time, often body sweat under the arms reading as explosives, according to German reports.

It's a very sensitive device, said one police official, and picks up traces of everything on a person's body. The machines were already controversial because of the depictions of human body. Now privacy group say the German experience shows the machines are little more than security theatre.

The German experience has demonstrated exactly how ineffective the devices are when they can't distinguish between body sweat and explosives or the pleats in a traveller's pants and an underwear bomb. It's not making anyone safer.

Passengers at New York airports said today they were surprised and concerned about the findings.

I didn't realize that they couldn't tell difference between arm sweat and explosives, so to me, very concerning as a traveller, I say, we should, reconsider.

The company that makes the body scan machines would not comment today while spokesman for TSA said the machines are the best they've got for now. And since last year, the technology has detected more than 300 dangerous or illegal items on airport passengers, fortunately no explosives, mostly drugs and knives, George.

OK, Brian, thanks very much.