Penetration testing is one of the priority areas in information security. It allows to perform an objective assessment of how easy it is to make unauthorized access to a computer system, as well as take a look at the system from the attacker’s point of view, namely, to understand how he can compromise the selected system, and what malicious actions he can perform. The paper describes the ways of overcoming installed security tools by an attacker, and a set of actions that he can do while having unauthorized access to a computer system. The most popular actions that are performed by attackers on a compromised system are: local elevation of privileges, theft of confidential information and data, user accounts, implementation of shadowing over the compromised user using the equipment installed on the victim’s system, which includes a microphone and web camera. To protect users from compromising their workstation, the article describes not only the actual methods of penetration by attackers into systems, but also the basic rules and recommendations on how users can increase security of their computer systems and reduce the probability of negative consequences from network attacks.