In the present article, the observer‐based proportional integral derivative (PID) security control problem is investigated for a networked system subject to aperiodic denial‐of‐service (DoS) attacks. First, by carefully modeling cyberattacks as aperiodic DoS attacks, a suitable switching observer is constructed to solve the state reconstruction problem. Second, to improve the utilization of network resources while resisting the impact of attacks, an adaptive event‐triggered communication protocol is introduced, whose trigger parameters can be dynamically adjusted according to the set learning rules. Third, based on the above analysis, an error switching system model is established, which describes the impact of the adaptive triggered protocol and aperiodic attacks in a unified framework. Then, by employing the switched system analysis method, sufficient conditions are obtained to ensure the error switched system being asymptotically stable. Furthermore, by means of orthogonal decomposition technique, a codesign method of the observer gains, triggered parameter, and PID controller gains is given. Finally, a simulation example is provided to illustrate the efficiency and applicability of the obtained results.