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Security Screening is one of the main operational responsibilities of CSIS and among its most visible functions. The goals of the Security Screening program are to assist the Government of Canada in preventing individuals who pose a threat to the security of Canada from either entering or obtaining status in this country; and to prevent individuals who pose such threats from obtaining access to sensitive government sites, assets or information. Security Screening serves as a first line of defence against both extremism and terrorism, as well as espionage and the proliferation of weapons of mass destruction. CSIS supports its Security Screening program in both Canada and through its liaison efforts abroad.