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In 1996, Congress decided that it needed a way to track people who overstay their visas — a huge and understated part of the nation's illegal immigration problem. So it authorized a program to verify that visa holders who arrived in the country eventually left it.

Five years later, on 9/11, terrorists tragically confirmed that program's failure by flying hijacked airplanes into buildings. Two of the 19 hijackers had overstayed visas. In the years that followed, the newly created Department of Homeland Security initiated what it called the United States Visitor and Immigrant Status Indicator Technology program (or US-VISIT for short) with much fanfare.http://blogs.usatoday.com/oped/2009/09/debate-on-visa-overstays-our-view-1-in-3-illegal-residents-arrives-legally-and-just-stays.html

USAToday Editorial

Interior Enforcement
visas
Attrition through Enforcement