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This work presented mathematical models and flow charts for implementing secure Proportional-Integral-Derivative (PID) algorithm in a process control loop. A number of security solutions have been recommended and some deployed in a process control system. Majority of these solutions are network based while others leverage on good security policy. A security solution based on network can be effective for securing control system from external threat agents who have to first of all, gain access to the control network. But for an internal threat agent or a disgruntled insider who does not only have the right privilege but also has a good understanding of the control system's operation, a network security is definitely not going to be effective. This work used system analysis to identify the possible things an internal threat agent can do to manipulate a control system using PID control algorithm as a case study. A secured PID mathematical model is proposed as a proactive mitigation technique to embedding security in a process control loop. As ongoing research, future work will concentrate on simulation and prototyping of the secured algorithm presented in this work. The proposed secured algorithm will not only serve as an additional security layer in industrial control system (ICS) but will also be relevant in the control domain of Internet of Things.