Omega Class Ai

"What humans have banned is AIs so powerful that they can single-handedly run and optimize an entire star system's economy, understand humans well enough to manipulate political systems, and seize control of entire military fleets. AIs of that caliber are universally banned (not to mention, expensive to build machines with the required capabilities).

Let's just say they had a bad experience once, and the more that is under direct control by AI, the more that could be controlled by such an AI. Those were called Omega class AIs, and only a handful were ever constructed." - Hazard

Lachesis was an omega class AI that caused significant troubles which lead to the banning of the technology.