Around 350,000 travelers arrive in the United States by air each day from Asia, South America and Africa. 65 percent of the undocumented immigrants who entered the United States between 2010 and 2017 arrived with full permission stamped into their passports. Some of the undocumented immigrants stay on as independent programming contractors after their visas have expired or after leaving a company that sponsored them for a visa. Developing policies to curb overstays requires accurate data and Homeland Security officials still lack a reliable system to track them. Many of those who overstay their visa do not intend to stay illegally. Graduates of American universities run afoul of deadlines or commit errors on immigration forms that automatically render them deportable. Sometimes employers transfer foreign workers to a new site and fail to amend their paperwork, as required, which also cancels their legal status.