Advances in information and communication technologies have led to a global information society and the emergence of a new digital world in which the development of each individual, communities, states, politics, and economics greatly depend on the use of telecommunications. At the same time global informatization allows to use new information and communication technologies to destabilize social situation in different countries, government authorities as well as to conduct illegal and destructive activities of political, criminal and terrorist organizations. In conditions of increasing instability of the situation in international relations and global economy there appear new challenges and threats to national security and sustainable development in Russia and other countries, including in the virtual environment. In this regard, the special relevance of the problem of cybersecurity for public authorities, economic entities and ordinary citizens in the processes of their interaction on the Internet, including ONS. The article puts forward a method of analysis of activity and identification of participants of the online social networks conducting illegal activity. Besides, it considers the structure of the information system of monitoring of their behavior.