ONI.SEC.PRTCL.1A is an Office of Naval Intelligence security protocol that restricts certain classified files and documents, or cancels searches for classified material.
First mention of the protocol was during a query by "Charlie Hotel 409871", better known as Doctor Catherine Halsey, head of the SPARTAN-II program. The protocol did not prevent her from accessing the last recorded message of Harvest's Agricultural AI Mack, but it did warn that her queries would be logged.
Much later, during the Battle of Earth in October, 2552, the Urban Infrastructure AI of the city of New Mombasa, the Superintendent, logged a single HEV pod crash into the city. It attempted to identify the object, checking first the New Mombasa Police Department records, and then attempted to access the UNSC files, but its search was halted by ONI.SEC.PRTCL.1A. This was possibly due to the fact that he wasn't a UNSC A.I., but just a Civilian one. Interestingly enough, in the trailer, "ONI.SEC.PRTCL.1A" is misspelled as "ONI.SEC.PRCTL-1A"