With the rapid development of the computer network technology, it has been widely used in various fields, and has achieved the good results. The network security has become a major obstacle that will affect the popularity of the network. Based on the author's practice of the computer network security defense for many years, the author carries out the detailed analysis of the problems of the computer network security and the characteristics of the risks, and focuses on the analysis of the main problems of the viruses and the hackers faced by the computer network, and proposes the concrete measures for the network security protection. With the arrival of the twenty-first century, the computer network technologies have obtained the rapid development, and the human society has entered the age of the Internet and the information, and the computer network is more and more widely used, so that the quality of our life can be greatly improved. However, with the rapid popularization and application of the computer network, the computer network security has become the focus of many experts and scholars. Especially with the taking-off of the modern Internet economy, the network security has caused great impact on the national economy and our life, which will more easily lead to Internet security incidents. In this paper, based on the author's practical experience of the computer network security precaution for many years, the author carries out the detailed analysis of the problems in the network security, and puts forward many measures for the network security precaution, to make efforts to the application of the computer network security.