Abstract: An intrusion detection system can be embedded in an industrial controller to detect an attack on an industrial control system. The intrusion detection system can detect an attack by determining if there are anomalies related to the network traffic in the industrial control system and/or by determining if the devices (e.g., sensors and actuators) connected to the industrial controllers of the industrial control system are not operating within expected ranges. To assist in determining if the devices of the industrial control system are not operating properly, the industrial controllers can also be networked together in a peer-to-peer network that permits each industrial controller to share its state information with the other industrial controllers.