A letter report issued by the General Accounting Office with an abstract that begins "Each year, millions of visitors, foreign students, and immigrants come to the United States. Foreign visitors may enter on a legal temporary basis--that is, with an authorized period of admission that expires on a specific date--either (1) with temporary visas (generally for tourism, business, or work) or, in some cases, (2) as tourists or business visitors who are allowed to enter without visas. (The latter include Canadians and qualified visitors from 27 countries who enter under the visa waiver program.) The majority of visitors who are tracked depart on time, but others overstay--and since September 11, 2001, the question has arisen as to whether overstay issues might have an impact on domestic security. In this report, we (1) describe available data on the extent of overstaying, (2) report on weaknesses in the Department of Homeland Security's long-standing overstay tracking system, and (3) provide some observations on the impact that tracking system weaknesses and significant levels of overstaying may have on domestic security."