The paper discusses a methodological approach to constructing models and algorithms for decision support when justifying the rational composition of a system for ensuring information security of a corporate computer network. In this case, the problem under consideration is represented in the form of a discrete mathematical programming model. A special feature of the model is the ability to take into account a wide variety of destructive impacts on a computer network and methods of protecting it. The generality of the model is also ensured by taking into account the possible nonlinear nature of the function reflecting the specific goals of creating an information security system. To solve the problem, a generalized algorithm has been developed that takes into account the features of the model. The general nature of the requirements for the parameters of the model and algorithm allows, on their basis, to form a fairly wide range of decision support techniques when justifying the rational composition of the information security system for specific variants of corporate computer networks and the conditions of their functioning.