threat defense

I usually as long as it is not used to the knowledge I have never how and in order to learn, so sometimes there will be some embarrassing things happen. The home, the children ran to me and asked me what is threat defense, I was really surprised, how could he have asked the threat defense, I asked how he knew about the threat defense, said he is watching TV when you hear, when I really do not know how to answer him, because I do not know how this threat defense, so I took the child said, the two of us go online to check the threat defense. After we checked, I only know what is this threat defense or, although children still do not understand this threat defense however, he could ask such a question, that he is still learning some knowledge.