Today, in absolute terms, not a single branch of the state can do without modern high-tech communications that connect computing systems and remote databases. The use of new information and communication technologies as a means of resolving contradictions, as well as a means of implicit influence, is becoming a growing threat to the security of the community on the world stage. The presented work examines not only the stages of development, but also the main trends, approaches to the construction of digital information systems, as well as the characteristic threats to information security for them. The article also shows the actual place of critical information segments in the general context of the communication system of the Russian Federation. The first part of the work reveals the concept of a three-component construction of regional critical information segments. The main part focuses on the difference in technologies used to build critical information segments. The main part of the article is aimed at identifying the vulnerabilities of complex information structures and systems that use the architecture of multiservice communication systems. The analysis carried out by the authors allows us to classify the main threats to information security both for communication systems built according to classical circuit switching schemes, and for communication systems based on new technological principles, basically - packet switching. In general, the authors tell us that the idea of a standard and clearly defined traffic structure and user interaction procedures, regardless of their type, geographic distance or area of its application, together with digital transmission and switching methods, has a revolutionary role in the development of communication systems. Special attention should be paid to the classification of protocols presented by the authors, which allows to identify the weakest points in modern information systems, which should be paid attention to first of all: protocols that ensure the functioning of wireless networks, mail protocols, file exchange protocols, and others
