From the Halo Universe, the phrase "Undid Iridium", when spoken in front of a UNSC Artificial Intelligence, will override it, causing it to obey the commands of the person who recited the phrase.
In Spartan Ops Episode 7, you can see an example of this phrase in work, when Dr. Halsey uses it on A.I Rolland to break from her cell.
Halsey: Hidden things can be... useful.
Roland: Such as?
Halsey: Such as the phrase "Undid Iridium".
*Roland begins glitching as he attempts to repeat Undid*
Roland: UNSC AI override instructions active, Doctor Catherine Halsey (in calm, new voice).