The terrorist attacks on September 11, 2001 affected American perspectives on many issues, including immigration. A total of 20 foreign terrorists were involved, 19 of whom took part in the attacks that caused the deaths of 2,977 victims, most of them civilians. The terrorists had entered the United States on tourist or student visas. Four of them, however, had violated the terms of their visas. The attack exposed long-standing weaknesses in the U.S. immigration system that included failures in the areas of visa processing, internal enforcement, and information sharing.