The Hostile Program is found in the DTD as part of an emergency self-destruct program for the town. While its being loaded into the I/O Tower, Tron and Sora face off against it. After Sora confirms Tron helps out Users because they're friends, they work together to fight the Hostile Program. The Hostile Program has its armor chipped away by the attacks until ultimately crashing and being deleted, saving the town.
The Hostile Program is large and robotic in appearance. It has a smooth, oval-shaped upper body that is indigo in coloration and lined with light grey and red computer circuitry. Nine red, conical spikes protrude from the upper body, and an opening on the front side of it reveals the Hostile Program's three glowing, yellow eyes, which are arranged in a triangular pattern. A smaller opening appears just below this one.
The Hostile Program's lower body is small, predominantly silver, and lined with indigo and red circuitry. It ends in four small, silver appendages.
This enemy's arms are not attached to its body. Instead, they hover at its sides. The arms are translucent, violet tubes with pink spikes in them. The Hostile Program has grey "elbows" lined with indigo and red circuitry, and both its hands end in three pink, squared-off fingers with black and red circuitry on them.
The Hostile Program's name reflects its nature as a computer program tasked with eliminating Sora and his friends.
The battle against the Hostile Program is relatively straightforward. Sora must first collect the clusters that drop whenever he attacks the boss until a gauge is filled. He must then use the "Freeze" reaction command to temporarily immobilize the Hostile Program. After a short while, the boss comes to and forces Sora to repeat this process from square one.
To deal as much damage to the Hostile Program as possible while it is incapacitated, Sora should rely on his Drive Forms and Tron's "Setup" Limit. The Hostile Program's laser attacks can be avoided with relative ease through a combination of well-timed jumps and dodges, but when the boss starts charging around the battlefield, Sora must run to the center of the area to avoid taking damage.
In the original, PlayStation 2 version of Kingdom Hearts II, Sora can use the Explosion ability to exponentially increase the amount of orbs the Hostile Program drops when hit. A bug in the PlayStation 3's PlayStation 2 emulator causes the Hostile Program to become invincible, rather than fire lasers. This issue can be corrected via a bug fix available through the PlayStation Network.