"Worm" (ワーム Wāmu) is a creation from Dr. Doppler in the Rockman X3 manga. The Worm can enter Reploids and disguise itself as chips, infecting the host with the Sigma Virus, leading to violent tendencies and also improving their abilities. When installed, the virus tries to break the host's will, not working well on exceptionally strong-willed Reploids, some being able to hold back and showing signs of their normal personalities.
When a worm infected X, he was temporarily paralyzed while stuck in an illusion where he lived in a peaceful utopia, but it transformed into a scorching barren land and his face changed. An angel appeared and said that X can't stay in the paradise due to his sins, many having fallen to his X-Buster, some even being old friends. As his sins can't be forgiven, he can only stay in a wasteland as a demon, but she offers to be always by his side to protect him, even if he becomes a Shura, being the only one to make company for him. Seeing that he can't go to paradise, X is tempted by her offer, but he realizes that something is wrong. X says that while he is currently walking the path of Shura, that doesn't mean he will become a demon, as he only uses his X-Buster to support others and what is on his heart. Seeing that X would not fall for the illusion, the angel is revealed to be Sigma, and X shoots him, breaking free from the illusion.
The Nightmare Police, Bit and Byte, are Reploids upgraded to have their bodies made entirely of Worms, granting them great power and allowing them to dismantle their bodies and move like Worms. Seeing them only as experiments, Dr. Doppler attacked the Nightmare Police alongside X and his friends, almost wiping them out. As they survived, Doppler decided to use Worms to upgrade them into "a powerful tool", turning them into Godkarmachine O Inary.