What is national security? National security is reduced for state national security. At present, national security threats can be divided into main enemies and potential ones and main enemies are separated inside and external ones. Arnold Toynbee said, "The destruction of the state is starting not from outside but from inside". This means we must be aware of inside enemies. How much do we know of the internal enemies who are trying to divide the people and overthrow the state? This paper focuses on corresponding strategies to depend our democratic state against inside enemies who penetrate all sectors of society and fabricate rumors, incite violence, and even try to overthrow our legitimate state with the base on the lessons of past West Germany case.