The term "illegal immigration" refers to the act of foreign nationals violating U.S. immigration policies and national laws by coming to and living in the United States without proper consent from the United States government. People become illegal immigrants in one of several ways. They can enter cross the border without proper authorization, arrive legally, but stay beyond the allowed period of time, or obtain a visa under false pretenses. Illegal immigrants are also referred to as illegal aliens. As of 2006, there were more than 10 million illegal immigrants living in the United States. Illegal immigration USA laws have been formed to protect the lawful citizens of the United States, and the immigrants who have arrived and stayed in the country legally. The United States uses barrier methods and patrol by U.S. Customs and Border agents to police the border, detect, and deter those who seek to enter the country illegally.