The considerable losses caused by the low levelof cyber security of companies, institutions and so on and the limited financial resources available imply the need to prioritize the implementation of measures to counter cyber attacks. For this purpose, the respective optimization problem is formulated as a Boolean mathematical programming one. At large dimensions, the use of known methods of solving the problem requires a large volume of calculations. That’s why, a simple rule for approximately solving the problem is obtained. By computer simulation, it is shown that the error of the solution when using this rule decreases considerably with the increase of the number of cybersecurity measures, more accurate – the more detailed such measures are. In order to reduce the error of solutions, three other simple algorithms are also proposed. The latter of these algorithms is more detailed and allows to reduce to a greater extent the solutions’ error.

The notion of “total favoring” of large or of small beneficiaries in proportional apportionments of entities is defined as a particular case of favoring. It is proven that the number of known conditions of total favoring of beneficiaries in an apportionment (APP) can be considerably reduced. Thus, the volume of calculations to be performed for the respective computer simulation was reduced. In order to quantitatively estimate the total favoring of beneficiaries by APP methods, three indicators were used: the percentage of apportionments, in which large beneficiaries are totally favored; the percentage of apportionments, in which small beneficiaries are totally favored; the percentage of total favoring of large or of small beneficiaries, depending on the APP method applied. A total of five APP methods are being researched: Hamilton (Hare), Sainte-Laguë (Webster), d’Hondt (Jefferson), Huntington-Hill and Adapted Sainte-Laguë. Based on results of computer simulation, the total favoring of beneficiaries by these five APP methods was estimated, including comparatively. For example, it has been identified that the d’Hondt method does not always totally favors beneficiaries to a greater extent than the Huntington-Hill method. At the same time, the Adapted Sainte-Laguë method always totally favors small beneficiaries less compared to the Huntington-Hill method.

Theoretical results not always give an unambiguous answer regarding the preference of using the indices of efficiency of investment in IT projects with equal lives. To complement some of such results, the Net Present Value (NPV), Profitability (PI) and Internal Rate of Return (IRR) indices are researched by computer simulation. In this aim, a model of comparative analysis of projects with equal lives is defined and the SIMINV application is made up. Using SIMINV, the percentage of cases when the solutions, obtained according to indices of each of the pairs {NPV, PI}, {NPV, IRR}, {PI, IRR} or of the triplet {NPV, PI, IRR}, differ for seven groups of alternatives of initial data is determined. Based on done calculations, some properties of indices were identified, including: the quantitative features and the character of dependences on initial data; the average percentage of cases with different solutions, which is of approx. 9 % for the pair of indices PI and IRR, and of 34-35 % for the other two pairs of indices specified above. On average, the solutions of comparing the efficiency of projects with equal lives, obtained using the NPV, PI and IRR indices, does not coincide in more than 1/3 of cases.

To quantitatively estimate the degree of favoring the beneficiaries in proportional apportionments of entities of the same kind (seats, PCs, etc.), five quantitative criteria were defined. By computer simulation, the degree of favoring the large or small beneficiaries by 6 apportionment methods is identified. Thus, favoring large beneficiaries by the d’Hondt method can overpass 10.7-12.1 entities (entities in excess) and that of small beneficiaries by the Huntington-Hill method -- 2.7-11.0 entities, and by the Adapted Sainte-Lagu\"{e} method -- 1.7-9.7 entities. The Huntington-Hill method favors small beneficiaries up to 5.70 times stronger than the Adapted Sainte-Laguë one does. Also, the d’Hondt method favors beneficiaries (the large ones) much stronger than the Adapted Sainte-Laguë one does (the small ones) -- for very many cases the respective ratio exceeds 10 times.

Theoretical results not always give an unambiguous answer regarding the preference of using the indices of IT project investment efficiency. To complement some of such results, the Net Present Value (NPV), Profitability (PI), Equivalent Annual NPV (EANPV)