The federal government classifies airline passengers who may be terrorist threats into three database categories:
550,000Approximate number of names on the Terrorist Identities Datamart Environment and Violent Gang and Terrorist Organization File lists. Inclusion on these lists does not guarantee flight restrictions but makes them subject to the next two lists.
number of names on the "selectee" list. These people have been targeted for additional screening and may undergo stricter searches, including body imaging and pat downs.
Approximate number of names on the "no fly" list. These people are never allowed to fly into, out of, or within the United States.
Source: Federal Transportation Security Administration; Congressional Sources