HKEY_LOCAL_MACHINE\SOFTWARE\Activision\Call of Duty United Offensive (on older 32-bit systems).

[COD] How to install the original COD on a PC with no disk drive

: Even on modern digital platforms like Steam, the game sometimes prompts for a key to access multiplayer servers.

Once you have a legitimate CD key, you cannot just plug and play on Windows 10 or 11. The original CD uses SecuROM, which is incompatible with modern OS security. Follow these steps: