The security of supervisory systems is vital for securing critical infrastructure, preventing cyberattacks, meeting regulatory requirements, and managing risk and resilience within system. This book will cover the introduction of SCADA (Supervisory Control and Data Acquisition) systems, the components within communicateCommunication with each other, and system design or architecture. Decoding the security vulnerabilities in these systems dealing both physical and cyber threats. The chapter provides a taxonomy of security threats such as viruses, worms, Trojan horses but also describes remedies by means of firewalls, access control, and encryption. It also discusses the difficulties of securing legacy SCADA systems. The chapter will provide readers with an overview of successful approaches to protecting these essential systems.