The original Manhunt has a unique history where the official version actually contains a pirate's work. Fully Cracked (historically and officially).
The retail version originally used SecuROM and hidden anti-piracy triggers that would break the game (e.g., doors wouldn't open) if the DRM was tampered with.
To bypass these issues for the digital re-release on Steam , Rockstar famously shipped the game with an existing crack from the scene group Razor 1911 rather than fixing the legacy DRM themselves.