A Corycaean was eavesdropping

Explanation

Menander mentions it in his Encheiridion. There were pirates around Corycus in Pamphylia, and certain men of Corycus, working with them, busied themselves with the cargoes of those sailing and the time at which they meant to sail, and reported to the pirates. Learning this, the merchants concealed many things. But when even so it became known to the pirates, the proverb gained currency for things thought to be done in secret but coming to be known.