WASHINGTON (AP) — The Obama administration is cracking down on immigrants in the U.S. who have overstayed the terms of their visas by using a system that automatically checks multiple national security, immigration and law enforcement databases at the same time, a senior Homeland Security Department official said.

The common practice has been to make manual checks of individual databases. The new system has already identified dozens of investigative leads, said John Cohen, deputy counterterrorism coordinator at the Homeland Security Department.

The immediate focus is on identifying people who have overstayed their visas and who pose a potential threat to national security or public safety, Cohen said.

Some of the 19 Sept. 11 hijackers were in the U.S. in violation of their visas, in some cases because they did not attend a school they said they would on their application for a student visa, or their visas had expired.

The 9/11 Commission saw the visa system as a major vulnerability and recommended completing a biometric system that would log immigrants out as they left the U.S. This program, however, was never fully implemented. Homeland Security Secretary Janet Napolitano has said the exit system called for by the commission is expensive.