But only a small percentage were arrested or denied entry to the United States, The Washington Post reported.

The database is maintained by the Terrorist Screening Center, which is under the joint oversight of the FBI and the Department of Homeland Security. Names on the list include those from the “no-fly” list maintained by the Transportation Security Administration, and lists kept by the State Department and FBI.

Federal officials say those in the database have been identified as potential terrorists and procedures exist to deal with those who should not be on the list. But others say the large number of hits without action indicates a problem.

"This really confirms the longstanding fear that this list is inaccurate and ultimately ineffective as an anti-terrorism tool," said David Sobel, a lawyer with the Electronic Frontier Foundation.