with rapid development of science and technology and the evolution of information revolution, International security environment is being reshaped. Important factors that determine national security competence—military operations, intelligence information on advanced weapons and enemy forces, economic activities that form the poles of national power, government's major systems—are exposed to hostile cyber attacks or accidental intrusions. Therefore, protecting information systems has emerged as an urgent national security issue. In particular, in waging wars, the concept of electronic/communications war that seek destruction of enemy command and control system, has been transformed into a more comprehensive and proactive concept of information warfare by the introduction of the cyber war doctrine. Information warfare encompasses pursuit of paralysis and destruction of a nation's all social infrastructure system and military control power. The existing concept of security strategy, which is a passive concept devised for protection of national information and information system, has been replaced by the proactive and aggressive concept of information warfare strategy. Information warfare seek early and effective victory by cyber attacks that can destroy the enemy's war capability and morale. Korea, which is a leader in information technology as well as a country vulnerable to attacks challenging information security, should prepare for information warfare of the twenty first century. Provision of more systematic and detailed measures—new response strategies, the establishment of national information security response system, creation or reorganization of institutions, and training of human resources—to cope with changes in international information security environment is called for. In addition, the private, public, and military organizations should work together to introduce joint defense strategies and organizations. As an organic integrated defense system has to be established, the government has to establish a governmental system for systematic system for threat assessment, judgment, and response. In particular, the role and responsibilities of the NSC should be upgraded. The government has been tilted toward domestic security and social issues as it responded to cyber crimes and terrors. Such tendency should be guarded against.