Cor Caroli V was a planet and the location of an outbreak of Phyrox plague in 2366. For unspecified reasons, Starfleet deemed the incident classified. Captain Jean Luc Picard mentions the incident to Haro, a Bolian Starfleet cadet he was imprisoned with. When Haro remembers details of the event, of which a first-year cadet would have no knowledge, Captain Picard realizes Haro is not who she claims to be (TNG episode: "Allegiance")