The security of critical infrastructures l … The security of critical infrastructures like water, gas or power grid control systems has been discussed more thoroughly in recent years due to recent events that have questioned their security. Terrorist groups are betting on cyber attack methods due to obvious advantages: it is cheaper than traditional methods, it is very difficult to be tracked, terrorists can hide their personalities and location, do the attack remotely from anywhere in the world, affect a large number of people, and finally, there are no physical barriers or checkpoints to cross. One has to understand that, despite some systems being considered
secure, attackers will continue to discover new vulnerabilities, to try new attacks and some of those attempts will succeed. One approach to address this
problem that is gaining momentum recently is intrusion tolerance. Based on this paradigm, there already are intrusion-tolerant network architectures that enhance the protection of critical infrastructures. However, even using such enhanced protection mechanisms, control systems remain with a certain level of vulnerability, which can be decreased if the process control software (PCS) itself is prepared to tolerate intrusions. This paper justifies the importance of developing intrusion-tolerant process control software and presents some insights on how to do it. nd presents some insights on how to do it.