The paper describes the mathematical aspects of an intelligent information decision support system (DSS) in the field of information security. A mathematical model of the system is presented. The reaction to a signal of a decrease in the level of security of IT assets is described. When the critical value of the objective function of security is reached, adjustments are being made to the list of information protection measures and review the current level of cyber risks. The system is configured so as not to trigger at the first, possibly random, external alarm. Also at the base of mathematical model there are financial restrictions of organization on ensuring the information security and prices for protection blocks are taken into account. This paper shows the connection of the presented mathematical model with classical linear programming problems. The mathematical formulation of this model is equivalent to the modified knapsack problem, a well-known discrete optimization problem; however, the presented mathematical model has its own specifics, which complicates the solution in the general case for arbitrary number of blocs and sections. In practical implementation, when this number of blocks and sections is not large, the problem, generally speaking, can be solved, among other things, by brute force method. It is shown that under some additional conditions, the problem can be reduced to the assignment problem, which is solved in polynomial time, and under additional conditions on the prices of protection blocks, its solution will the identical permutation. These additional conditions are not contrived or artificial.