There is provided a packet monitoring apparatus for monitoring packets copied from an industrial control system (ICS) network, the apparatus being configured to perform an analysis of a plurality of packets copied from the ICS network and generate a digital command signal responsive to the analysis for transmission via a digital input/output channel. There is also provided an active prove that is configured to generate and transmit at least one query packet into the ICS network responsive to a digital command signal, optionally received from the packet monitoring apparatus.