New York Police Department tactical police officers stand guard near the New York Stock Exchange on September 9, 2011 in New York City. Officials are stepping up security in New York and Washington D.C. a day after U.S. officials received a credible but unconfirmed terror threat to utilize car bombs on bridges or tunnels in New York or Washington. (Photo by Justin Sullivan/Getty Images)

Afghan police officers secure a transportation headquarters that was besieged for two days last weekend, on May 14, 2011 in Kandahar, Afghanistan. Taliban gunmen and suicide bombers unleashed a major assault May 7, 2011 on locations in Kandahar that included the governor's compound, the mayor's office, police stations, and an intelligence agency headquarters. (Photo by Majid Saeedi/Getty Images)

A screen shows the new Automated Target Recognition software as a TSA employee, who couldn't provide her name, waits to walk into the advanced imaging technology unit to demostrate the new software that has been installed at Miami International Airport on August 23, 2011 in Miami, Florida. The new software is designed to enhance passenger privacy by eliminating passenger-specific images and instead auto-detecting potential threat items and indicating their location on a screen which shows a generic outline of a person. (Photo by Joe Raedle/Getty Images)