A tamper-proof lock includes: a housing, shaft/handle, cam, lever, spring, and plate. The shaft is pivotally mounted in a housing orifice, with the cam pivotally mounted to the shaft. The cam has first and second shaped openings at first and second respective radial positions, and an arcuate recess. The lever is secured to the shaft, and has a protrusion that alternately engages each of first and second ends of the arcuate recess to respectively/selectively drive the cam to rotate/counter-rotate in first and second directions, into locked and unlocked cam positions. The spring biases the plate for a protrusion thereon to be respectively received within each of first and second shaped cam openings, when aligned therewith at those cam positions, and for a curved surface of the plate to be correspondingly received within first and second curved cam recesses, respectively, when aligned therewith, which facilitate withdrawal of the plate protrusion.