  This paper proposes a data-driven framework to identify the attack-free
sensors in a networked control system when some of the sensors are corrupted by
an adversary. An operator with access to offline input-output attack-free
trajectories of the plant is considered. Then, a data-driven algorithm is
proposed to identify the attack-free sensors when the plant is controlled
online. We also provide necessary conditions, based on the properties of the
plant, under which the algorithm is feasible. An extension of the algorithm is
presented to identify the sensors completely online against certain classes of
attacks. The efficacy of our algorithm is depicted through numerical examples.
