In this June 27, 2006, file photo U.S. military guards walk within Camp Delta at the Guantanamo Bay U.S. Naval Base, Cuba. The U.S. announced the transfer of four detainees from Guantanamo to Oman; one will go to Estonia. Brennan Linsley/AP hide caption

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Abu Hamza al-Masri, also known as Mustafa Kamel Mustafa, at a 2002 fundamentalist Islamic conference in London, where he condemned what he called oppression of Muslims in the West. Masri was sentenced Friday in U.S. court to life in prison on terrorism-related charges. Alistair Fuller/AP hide caption

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The Terrorism Risk Insurance Program guarantees insurance payments in case of a terrorist attack at places like shopping malls, big-city high rises, and events like the Super Bowl. Jamie Squire/Getty Images hide caption

itoggle caption Jamie Squire/Getty Images