In 1943 the Allied forces of America and Great Britain were preparing to invade the island of Sicily. To keep the invasion secret, they orchestrated their own security breach. The Allies sent a body floating toward German/Italian occupied territory with documents detailing a fabricated Allied invasion of Sardinia and Greece. The Germans found the body and plans and accepted the false plans as true. As a result, the Allied invasion of Sicily was mostly a surprise to Axis command.
After the invasion, whenever actual Allied planes landed in German hands, they would often refuse to believe them, assuming they were simply another Allied ruse.