A threat detection system for industrial controllers, comprising: at least one Programmable Logic Controller (PLC); at least one physical device connected with the PLC; a Deterministic Fictitious Programmable Logic Controller (DFPLC) deterministically programmed to respond with at least one predetermined signal to at least one input signal received; and a monitoring unit connected with the DFPLC; the DFPLC disguised as a PLC; and the monitoring unit configured to send at least one input signal to the DFPLC, receive at least one response from the DFPLC and communicate at least one alert upon the at least one response being other than an expected response according to the deterministic programming of the DFPLC.