In July of 1955, Lewis Strauss, Chairman of the Atomic Energy Commission, wrote to CIA director Allen Dulles over matters of mutual interest. In one of those letters, uncovered in the Agency’s archives, Strauss thanked Dulles for a package he had sent him, using deliberately vague terms to describe its contents as to “avoid classifying this letter.”

Strauss’ efforts were in vain, however. Not only was the letter classified for just shy of 50 years, but the vague descriptor itself remains classified to this day.

The lesson here? Don’t tell the CIA what not to classify. They’re gonna classify everything.

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