Bruce Schneier linked to this post today and I’m doing the same. He didn’t quote from the article, but I’m going to quote two paragraphs, just to give you an idea, since I’m not Schneier and you won’t take my word for it.
At this moment, there are roughly 5000 commercial airliners in the skies above you. There will be 28,000 flights today, and 840,000 in the next month — every month. The U.S. fleet consists of some 6000 aircraft — almost all of which will be parked unattended tonight at a public airport. We will carry almost 7 billion passengers this year, the number increasing to 10 billion by 2010, barring an exogenous event like another 9/11.
There is simply no deployable technology that has a prayer of keeping a motivated, prepared terrorist out of the system every time — even most times. TSA misses more than 90% of detectable weapons at passenger checkpoints in their own tests, and it is not their fault, because of the limitations of technology and the number of inspections they must conduct. This doesn’t count several classes of completely undetectable weapons like composite knives and liquid explosives.
I urge you to read the full post, it’s fascinating, enlightening, and chilling.