This thesis defines the concept of security, cyber security, security rules and security systems and explains how to implement security rules and systems in small and medium enterprises. The aim of this paper is to raise awareness of the importance of security and safety in small and medium enterprises and to determine which security rules and security systems are important for enterprises and whether their implementation will reduce the risks of adverse events that could harm digital business. Due to the lack of resources and knowledge, small and medium enterprises do not make enough efforts to protect themselves from various types of risks to employees and assets of enterprises. Precisely due to the fact that small and medium-sized enterprises do not continuously apply and develop security rules and systems, enterprises are becoming an increasingly interesting target for various attackers and harmful events are increasingly occurring in enterprises. This paper will explain security rules and systems and their application in companies. Also, an analysis of selected adverse events in companies will be conducted to determine whether safety rules and systems have been implemented in companies, or whether their application would reduce the risk of adverse events.