Unless he lives in a nation that doesn't enforce intellectual property rights.

The Civil Code of the Russian Federation Chapter 70. Copyright.

Article 1280.
Free Reproduction of computer programs and databases. Decompilation of Computer Programs.
1. Person lawfully in possession of a copy of a computer program or database instance (the user) may,
without the permission of the author or copyright holder and without payment of additional remuneration:
1) make changes to the computer program or database solely for the purpose of their operation on the
user's device and to perform any actions necessary for the functioning of such a program or database
according to their function, including storing in computer memory (one computer or a network), and to
make correct obvious errors, unless otherwise provided by contract with the copyright holder;
2) make a copy of a computer program or database provided that the copy is intended solely for archiving
purposes or for replacement of a lawfully acquired copy where such copy has been lost, destroyed or
unusable; at the same time a copy of a computer program or database may not be used for purposes other
than those specified in paragraph 1 of this paragraph, and must be destroyed if possession of the copy of
such a program or database cease to be lawful.
2. Person lawfully in possession of a copy of a computer program may, without the consent of the
rightholder and without payment of additional remuneration: to study, investigate or test the functioning
of such a program in order to determine the ideas and principles which underlie any element of a computer
program through any action under subparagraph 1 paragraph 1 of this article.
3. Person lawfully in possession of a copy of a computer program may, without the consent of the
rightholder and without payment of additional compensation: to reproduce and convert the object code
into source code (decompile the computer program) or by third parties to carry out these actions, if they
are necessary to achieve interoperability independently developed that person's computer program with
other programs that can interact with the decompiled program, under the following conditions:
1) the information necessary to achieve interoperability, has not previously been available to that person
from other sources;
2) these actions are carried out in respect of only those parts of the decompilation of computer programs,
are necessary to achieve interoperability;
3) information obtained by decompilation may only be used to achieve the ability to interact independently
created computer programs with other programs that can be transferred to other persons, except where
necessary to achieve the ability to interact independently created computer programs with other programs
and can not be used to develop a computer program, a type essentially comparable to the decompiled
computer program, or for any other act that violates the exclusive right to the computer program.
4. Application of the provisions stipulated in this Article shall not cause undue damage to normal use
of a computer program or database, and should not unreasonably prejudice the legitimate interests
of the author or copyright holder.