Theoretical issues related to the architecture and operating principles of attack detection and prevention systems in computer networks are outlined. Methods, techniques and tools used to protect computer systems and networks from attacks are presented. The content of the textbook corresponds to the program and courses of lectures read by the author at the Moscow Pedagogical University named after N.E. Bauman. For students studying in the field of preparation “Information security of automated systems”, as well as students of the faculty of advanced training. May be of interest to specialists in the field of using modern means and methods of ensuring information security.