The amounts of “material unaccounted for” were classified by the AEC.
Using this device he was able to store hundreds of thousands of classified documents in decrypted form.
He put American and other lives at risk with some of his 2010 leaks of classified military material.
"arranged in classes," 1828, past participle adjective from classify. Meaning "secret" (of government information) is from 1941, American English. Classifieds (n.) "newspaper advertisements arranged by classes," 1913, is short for classified advertisements