Abstract: This paper discusses the challenge and tactics that reply to electromagnetic compatibility field in the times of information. The paper proposes the idea that the basis of information security is the EM security of the information network and equipment. The paper puts forward a principle model of the leakage of EM information by the unintentional electromagnetic radiation from electronic equipment. The paper analyses EM security problems caused by the unintentional electromagnetic radiation existing everywhere, summarizes the present and trends of the TEMPEST computer, and predicts the future trends of EM security problem in the areas of robot, wireless networks, cabling networks, and the industrial networks. At last, the author look into the developing EM security and safety EMC standards and elaborate the threatening situation to the national critical infrastructure networks when facing the attack of EM information security offensive has become a super weapons.