As we live in the 21st century, so called the "Information Age", network has become a basic establishment. However, we have found the different face that it also has been used as a tool of a unauthorized outflow and destruction of information. In recent years, beginner could easily get a hacking and weakness reference tools from internet. The menace of the situation has increased; the intellectual diverse offensive technique has become increasingly dangerous. The purpose of the thesis is to detect a abnormal packet for networking offense. In order to detect the packet, it gathers the packets and create inspection information that tells abnormality by using probability of special quality, then decision of intrusion is made by using a neural network.l network.