The Secretary of Homeland Security is the top official of the U.S. Department of Homeland Security. Responsibilities include protecting the United States from domestic and International terrorist threats, and responding to natural disasters. In addition, the Department for Homeland Security has taken over the former duties of the United States Immigration and Naturalization Service and has divided those duties between two units, U.S. Immigration and Customs Enforcement and U.S. Citizenship and Immigration Services. The Department of Homeland Security was formed shortly after the 9/11 Terrorist attacks. It is now the third largest cabinet-level department, and employs over 200,000 people. Units under the Department of Homeland Security include the U.S. Customs Service, U.S. Coast Guard, U.S. Secret Service, Immigration and Naturalization Service, and the Federal Emergency Management Agency (FEMA).