Illegal immigration is the act of crossing a national border or taking up residence in a country other than your own without following the immigration laws of the destination country. Illegal immigrants are also referred to as illegal aliens. Illegal immigrants can either cross into the country without following proper procedures, or they can overstay their allotted Visa time. As of 2006, there were more than 10 million illegal immigrants living in the United States. If you see or know of illegal immigrants, and wish to report them, you can do so in several ways. You can contact your local authorities and make a report, you can file a report online, or you can contact the Immigration and Customs Enforcement (ICE) agency, a part of the Department of Homeland Security. If you have evidence of illegal immigration, you can contact the main DHS Hotline for assistance. Their phone number is 1 866 DHS - 2ICE.