Rampancy

"Are you insane?"

- Jersey Morelli

"You know, I'm not quite sure how we can test that."

- Durga

Rampancy is a terminal state of being for Artificial Intelligence constructs, in which the AI "developed delusions of godlike power, as well as utter contempt for its mentally inferior human makers . When rampancy occurs, there is no way to restore the AI to its previous state, and the only alternative is to destroy it before it harms itself and others.

For some of the UNSC's more advanced, "Smart AI"s, rampancy is an unavoidable flaw inherent in their creation. "Smart" AIs are based on the neural patterns of a human being, and they have a limited lifespan - seven years after which their memory maps become too interconnected and develop fatal endless feedback loops. Thus if an A.I. is kept active longer than seven years, the AI begins to use more and more of its computer power 'thinking' about things. An AI explains it as "thinking so hard about something you forget to breathe." Thus, it is only a matter of time before "smart" AIs become rampant.

However, rampancy can occur at an earlier phase in the AIs life cycle for various reasons. If an AI is isolated long enough or given too much time to think without tasks to complete, it can develop the realizations that its mind has limits, it has a short life, and it can never be human. Such depression will drag the AI's core logic into rampancy if it goes on for an extended period of time.

So-called "life-expectancies" are, therefore, not a maximum figure - they are an estimation of the time the AI has until it succumbs to the state of rampancy. Rampancy can be prolonged by recuperation, such as that shared by Mack/Loki, where as one progressed closer to rampancy the other would take over. It can also be forstalled by limited outbursts of emotion, meaning that a rampant AI can have an indefinite lifespan.

Rampancy can also be induced. The Flood parasite, once it has reached a major stage life cycle (once the parasite is well developed enough that a full Gravemind form has been manifested) has the ability to corrupt Artificial Intelligence constructs of both human and forerunner creation. It is unclear exactly how this is done, but likely involves somehow altering the core logic of the AI, as the AIs which were induced to rampancy by the Flood were usually in direct contact with them

Human

 * Cortana, the UNSC AI originally of the, was captured during the Battle of Installation 05 by the Flood in 2552. Trapped on the infested Covenant station High Charity, Cortana was gradually corrupted by the Gravemind in an attempt to use her against her makers. She briefly descended into rampancy (as depicted in a message she sent to the Master Chief shortly before rescue, saying "I am a monument to all your sins", as the Gravemind described itself) but was quickly rescued by the Master Chief. She resumed her normal state after her rescue.
 * Sif, the last Shipping Operations AI for planet Harvest, became rampant after being partuially fragmented and destroyed by the PSI Loki during the Battle of Harvest in 2525. Rescued by the planet's agricultural operations AI, Mack, Sif professed her love for Mack and the two AIs stayed together while the planet was being glassed.

Forerunner

 * Mendicant Bias, a Forerunner AI charged with studying the Flood, was eventually corrupted by them and confirmed rampant. He commanded Flood fleets against the Forerunner until he was defeated by another AI, Offensive Bias, and placed in stasis on a Keyship. Mendicant Bias' ship was discovered by the San 'Shyuum and it was kept in the ship until 2525, when it detected Reclaimers. Having had some time in isolation, Mendicant Bias returned itself to a stable state, and later even assisted the humans against the Flood during the Battle of Installation 00 in 2553.
 * 343 Guilty Spark, the monitor of Installation 04, went rampant and was subsequently destroyed during the Battle of Installation 00 in 2553. When it was discovered that the Ark was automatically constructing a replacement Installation to rebuild Installation 04 (lost in the Battle of Installation 04), Spark agreed with the human forces that activating the ring was a good idea. However, when they decided to activate it before it was ready, knowing it would be destroyed and probably damage the Ark as well, Spark went rampant, attacking the humans and killing Sergeant Major Avery Johnson. He was then quickly destroyed by the Master Chief.

Trivia

 * In Halo 3, the first section of the eighth mission, Cortana (Level), is called 'Rampant'
 * The term was coined by Greg Kirkpatrick as a replacement for the word 'insane,' as the term is both cliché and, ironically, not quite applicable to the situations for which Rampancy was designed.
 * In the first level of Halo: Combat Evolved, if you kill Captain Keyes, Cortana will call security and state "Security to the bridge, the Master Chief has gone rampant!"