Security measures Computer networks -- 12 Prevention 11 Terrorism -- 11 Computer security 9 Aeronautics, Commercial -- 6 Hijacking of aircraft -- 4 more ... National security -- 4 Airports -- 3 Data protection 3 Hijacking of aircraft 3 Merchant marine -- 3 Prevention. -- 3 Security measures -- 3 Terrorism 3 War on Terrorism, 2001-2009 3 Evaluation. -- 2 Government policy -- 2 Industries -- 2 Information warfare -- 2 Military policy 2 Safety measures 2 Transportation -- 2 Access control 1 Air power -- 1 Astronautics and state -- 1 Asymmetric warfare 1 Boats and boating -- 1 Buildings -- 1 Civil defense 1 less ...