I think this was in Costello’s Pacific War book. The undetected Japanese spies were scooped up with the loyal citizens when the Japanese were incarcerated

The best indication of how impotent Axis spies were in 1942: in Stanley Johnson’s (author of Queen of the Flat Tops) 1942 article on Midway he divulged that the USN was reading the Japanese Navy codes. King wanted Johnson keelhauled. The authorities in Japan never found out.