Due to the fierce competitive global market, enterprises need to face and overcome new challenges and requirements to stay ahead of competition. Cyber-physical systems, Internet of things, and digital twins are some of the contemporary technologies that are used in the context of Industry 4.0 in order to instill intelligence into the industrial sector by changing traditional manufacturing to smart manufacturing. The digitalized and interconnected nature of Industry 4.0 creates new security, privacy, and safety challenges that need to be addressed in order for it to be fully realized.This study presents an overview regarding the use of digital twins as a means to reinforce and secure cyber-physical systems and Industry 4.0, in general. Digital twins connect the physical and virtual worlds and can be used in combination with other technologies to provide several merits in various sectors, such as real-time monitoring and controlling, prompt access to dynamic data, constant visualization and analysis, process optimization, advanced decision-making, and prediction systems. All in all, based on the literature review, digital twins can constitute an essential tool for the realization, reinforcement, and security of cyber-physical systems and Industry 4.0.