Problematic issues of information security of cyber-physical systems

This paper is an analysis and systematization of modern research in the field of cyber-physical system information security. The problematic issues of information security of such systems are considered: «what is being attacked?», «who is attacking?», «why is someone attacking?», «how is someone attacking?» and «how to protect the system?». As an answer to the first question, the paper proposes a definition and classification of cyber-physical systems according to such criteria as complexity, connectivity, criticality and social aspect. As an answer to the second and the third questions, the paper describes a classification of attacker according to such criteria as type of access, method of access, intentions, knowledge and resources. As  an answer to the fourth question, the paper contains a classification of attack actions according to such criteria as subject and object, method of influence, prerequisites and consequences. As an answer to the fifth question, the paper proposes a classification of protection methods and security tools according to such criteria as principle of operation, object of protection and task to be solved. The scientific significance of the paper is systematization of a current state of the art in the subject area. The practical value of the paper is providing information about security issues that are specific to cyber-physical systems, which will allow one to develop, manage and use such systems in a more secure way.