An industrial control system (ICS) automates and controls industrial processes (e.g. manufacturing, product handling, production, and distribution) and mechanical functions to keep processes and machinery running smoothly. An ICS may support critical infrastructure (e.g. energy and utilities, transportation, health, manufacturing, food, and water) that is essential to the ongoing safety, security, and well-being of Canadians. An ICS is the base controller for the other layers in an infrastructure (i.e. production, office, enterprise), therefore it should be secured to maintain functionality. This document introduces some ICS security threats and risks and the security measures that you can implement to protect these systems from harm.