WASHINGTON -- A State Department official says the U.S. has revoked more than 122,000 visas since 2001, including 9,500 because of the threat of terrorism.
Michele Thoren Bond is assistant secretary for the Bureau of Consular Affairs. Bond says security reviews don't stop when a visa is issued to someone.
She says the U.S. continues to match new threat information with the records of visa waivers and revoke visas if necessary based on that information.
Bond spoke Thursday to members of the House Oversight and Government Reform Committee examining safeguards to keep extremists from exploiting legal paths to travel to the U.S.
San Bernardino, Calif. Shooter, Tashfeen Malik, came to the U.S. on a K-1 fiance visa last year as Syed Rizwan Farook's wife despite the fact that the FBI believed she was already radicalized.
Lawmakers have since been demanding answers about how Malik got through what is said to be a rigorous screening process.
Malik had been interviewed at the U.S. embassy in Pakistan and vetted by five different government agencies, CBS News' Margaret Brennan reported earlier this month.
Malik's name and picture were checked against a terror watch list and her fingerprints were searched in two different databases.
Nothing found during those checks and interviews suggested she would commit an act of terrorism by killing people on U.S. soil.
The K-1 U.S. consulate interview generally involves probing questions about the relationship between the couple -- how many times they have met, details about the proposal and wedding, evidence that there is a real relationship between the two.
In her fiancée visa interview, Malik was asked about her husband's job as a food safety inspector in California, his birthday and financial records. She also supplied the visa official with pictures of their engagement ceremony in Mecca, a U.S. official told CBS News.
University of Virginia Law Professor David Martin, a veteran of the Homeland Security, State and Defense departments, said there's no easy solution to closing the gaps in the system, but thinks the best way to improve security in the program is to improve the intelligence collection that helps the U.S. create databases it uses for background checks.
"They're never going to be foolproof," he said, noting that someone like Malik - who appeared to make an effort to mask her growing radicalization - can "stay out any situation where our intelligence capacities or the capacities of the countries where they're from or where they're temporarily living would have any reading on them."
Joe Cuddihy, a consultant at McConnell International who previously worked in DHS and DOJ, thinks the U.S. should take another look at the way information is passed between DHS and the State Department during the visa application process, demand more extensive information and verification about the applicant's recent travels, and apply information gathered by the U.S. military and other agencies on the ground in foreign countries.
The U.S. visa program has been overhauled before. The foreign-born perpetrators of the 9/11 terrorist attacks arrived in the U.S. on legal visas, and only two of them were no longer valid by the time of the attacks. In May 2003, the State Department began requiring a personal interview with a consular officer for all visa applications, a process that was written into law by Congress in 2004. The government expanded the use of background checks and improved tracking for visa holders already in the U.S.
For now, the program is being reexamined by Congress and the federal government. The House -- on Tuesday, December 8, 2015 -- overwhelmingly passed legislation to bolster the U.S. visa waiver programafter officials noticed it contained loopholes after the Nov. 13 Paris terror attacks.