classified

Sorted into classes or categories.

Formally assigned by a government to one of several levels of sensitivity, usually (in English) top secret, secret, confidential, and, in some countries, restricted; thereby making disclosure to unauthorized persons illegal.

We do not discuss specific interrogation techniques because they are classified information.

Charlie: Where did you see this? Maverick: That's classified. I could tell you, but then I'd have to kill you. Charlie: I have Top Secret clearance. The Pentagon sees to it that I know more than you.

Not meant to be disclosed by a person or organization.

I won't say who I'm going to the prom with; that's classified.

A classified advertisement in a newspaper or magazine.

He ran a classified for the tools he wanted to sell.