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A security failure is a failure caused by a deliberate human action. Many systems are exposed to a number of threats. The threats may be related to physical actions or cyberattacks. Physical threats include arson, sabotage, theft, and many more. A cyberattack is only relevant for systems that are connected to a cyber network (e.g. Internet, or mobile phone network). A threat may be used by a threat actor to attack the system. The system may have a number of vulnerabilities (i.e. weaknesses) that may be exploited by the threat actor to make a “successful” attack.

With the development of new technologies, such as cyber‐physical systems, the Internet of Things (IoT), smart‐grids, smart cities, remote operation and maintenance, and many more, cyberattacks come more frequently and we can now hardly open a newspaper without articles about cyberattacks. Many of these attacks are directed toward critical infrastructure and industrial control and safety systems.

The structure of a security failure is illustrated in Figure 3.11. A threat, a threat actor, and a vulnerability are required “inputs” for a security failure. The threat actor uses a threat to attack the system, and the threat inspires the threat actor. The attack can only be successful if the system has one or more vulnerabilities.

A security failure is not a random event, but the consequence of a deliberate action made by the threat actor. To reduce the likelihood of security failures, vulnerabilities should be identified and removed during system design.

Figure 3.11 The structure of a security failure.