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In the wake of Umar Farouk Abdulmutallab's alleged attempt to blow up a transcontinental airliner over Detroit on Christmas Day, President Obama ordered on Sunday a review of two major components of airport security: watch lists and the equipment used at airport checkpoints. After a comment by his father, Abdulmutallab was put on a list of 550,000 people with alleged terrorist connections, but not the no-fly list of 4,000, meaning that he was able to board the airplane despite using cash to buy a ticket and checking no bags. A new security-screening device that uses so-called milimeter waves to create an image of a passenger's body underneath the clothing could have helped catch Abdulmutallab, but only 40 machines have been installed at 19 airports across the U.S. Privacy advocates are trying to slow the technology's introduction, and there is pending House legislation that would prohibit the equipment for routine passenger screening.