In the article some aspects of the professional activity of the teacher of informatics in the sector of information security are analyzed. It is noted that the processes of informatization of the modern society and education cause the aggravation of the problem of information security. It is emphasized that the modern teacher of informatics plays a special role in the issue of information security. The teacher forms the skills of informational activity of students, from the skills and ethical use of information materials to the principles of creating their own resources and programs. A competent teacher must be a standard of the subject of secure information activity and at the same time must pay students' attention on the issues of information security in all aspects: pedagogical, psychological, legal, technical. The purpose of the article is to identify the peculiarities of the professional activity of the teacher of informatics in the sector of information security. Objectives of the article: 1) to analyze the content of the activity of the teacher of informatics in the sector of information security; 2) to consider the notion of informational culture of the teacher of informatics as a necessary component of the professional activity of a specialist in the sector of information security. Methods of research: theoretical analysis and synthesis of psychological and pedagogical literature in order to find out the content of the professional activity of the teacher of informatics and the phenomenon of information culture; generalization in order to determine the knowledge, skills and abilities of the teacher of informatics on the basis of studying of educational programs of training of specialists. It is substantiated that activity of the teacher of informatics in the sector of information security involves implementation of the preventive measures concerning safe information work at different levels (personal, group), definition of a rational system of information protection in the specific conditions of pedagogical work using modern information and communication technologies, etc. In this case it is necessary for teacher to possess a high level of information culture, aimed at the implementation of professional functions through the application of the latest information and communication technologies with the mandatory provision of information security requirements. The components of information culture of the teacher of informatics are: information-legal, program-technical, socio-cultural.