The use of AIT scanners has increased since the Christmas Day 2009 attempt by Umar Farouk AbdulMutallab to blow up a plane over Detroit by detonating plastic explosives hidden in his underwear.

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Plenty of warning signs also preceded Nigerian Umar Farouq Abdulmutallab's attempt to blow up Northwest flight 253 over Detroit on Christmas Day 2009 with an underwear bomb made with PETN, a plastic explosive that was not detected by airport security.

CNN: Agencies often miss warning signs of attacks

We were lucky that the "shoe bomber" failed to ignite the plastic explosive in his sneakers, lucky that the "underwear bomber" similarly botched his crotch bomb, and lucky that the "Times Square bomber" bollixed up the timer for his car full of explosives.

CENTERFORSECURITYPOLICY: Center For Security Policy