not meant to be recorded or reported as official

confidential

(that is to be) kept from the knowledge or view of others; of which others have no knowledge

hidden, unrevealed

(having the habit of) hiding one's knowledge, feelings etc

uncommunicative

underground

hidden, underground

(of actions) done secretly

sneaky, secret

not communicative

shy, silent

acting secretly

secret, spy

deceitful(ly)

deceitful