From Halopedia, the Halo wiki
Article 428-A is a UNSC protocol in effect in 2552. The protocol forbids soldiers from discussing matters related to classified missions to any personnel who do not have the clearance. This includes anyone, even an AI, who questions the soldier or marine before they are debriefed. Violation of this protocol requires the person questioned to report the offense to their superior officer and are possibly court martialed or even put to death.
List of appearances