FBI's Security Watch Lists Explained

Umar Farouk Abdulmutallab was known to U.S. officials before he boarded Northwest flight 253 with a bomb packed in his underwear. His name was one of more than 500,000 in a broad terror data base at the National Counterterrorism Center.

But Abdulmutallab's was not flagged as a threat and his name was never forwarded to the FBI, which manages the government's three security watch lists, reports CBS News Correspondent Bob Orr.

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The largest, the Terrorism Watch List, has about 400,000 names, a population that would more than fill four Rose Bowls. People on this list have raised "a reasonable suspicion" of terror connections. They can still fly but are carefully checked.

Names that trigger even more red flags are moved to a second, more restrictive category, the Selectee List. It numbers about 14,000, enough to fill the end zone of one Rose Bowl. A "selectee" must undergo more thorough screening and pat downs.

The highest priority, the no-fly list, has just 3,400 names, enough to fill one stadium section. Those on the no-fly list have established terror ties and cannot fly into the U.S.

Since the Detroit attack, the White House has ordered a review. Sources say the National Counterterrorism Center has now sent hundreds of new names to the FBI, and the FBI has upgraded "hundreds of names" from the master watch list to the Selectee category.

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But, for intelligence officials, it's a daunting challenge trying to identify the true terrorists among a mass of suspects.

"There isn't a magic formula or a magic Google program that will then spew out a defined list of bad people," CBS News National Security Analyst Juan Zarate told Orr. "There has to be a human component here, and there's judgment at play and that judgment can be faulty, and we saw that in this recent case of Abdulmutallab."

Officials say no watch list is perfect, but as a first line of defense it has to be better than it was on Christmas Day.