A complex adaptive system is a network of many interacting parts that changes its behavior through feedback. The whole system does not follow one fixed script; instead, patterns emerge from local decisions, dependencies, and repeated adjustment. In security, this matters because attackers, defenders, users, and infrastructure all influence one another, so small changes can produce unexpected effects.
Cyber attacks often behave like complex adaptive systems: phishing, credential abuse, malware, and command-and-control infrastructure shift in response to detection, blocking, and takedowns. Defenders face the same reality when tuning alerts, isolating hosts, or changing access controls, because attackers adapt to new barriers. This is why rigid plans can fail in incident response. Effective security programs use monitoring, rapid feedback, and layered controls to stay resilient as the environment changes.