Files pre-compiled to help the emulator run the game without the "stuttering" common in emulation. The Risks of "Highly Compressed" Links

Highly compressed files may have certain assets (like radio stations or cinematics) removed to save space, potentially leading to game crashes. How to Play Forza Horizon 1 on PC

Consequently, the "PC version" people search for is actually the original Xbox 360 ISO file running through an emulator, specifically

These files often require disabling antivirus software, making the system vulnerable to trojans or miners.