Upon realizing the threat of both Tron and Sora, the Master Control Program, or MCP, had Sark deploy a special program virus called the Hostile Program. It caused chaos for the computer world as well as the real world in Hollow Bastion. Eventually Sora and Tron encountered the Hostile Program. The Hostile Program spotted the two, and processed to fight them. After a long battle, the Hostile Program was defeated. After defeating the Hostile Program Tron gives Sora the Photon Debugger Keychain.
- The Hostile Program is one of the few bosses in Kingdom Hearts II that isn't a Heartless, a Nobody, has nothing to do with the Heartless, or anything to do with Organization XIII.
- The program's actual name is unknown, as "Hostile Program" is just a descriptive term that Tron and Jiminy call it.