If you want to play the original MW3 safely, here are your only legitimate options as of 2021 (and still valid today):
In 2021 alone, security firms reported a 45% spike in gaming-related malware, with “free COD downloads” being a top vector.
Downloading "codepregfxff" in 2021 was a game of Russian roulette with a fully loaded magazine. Here is what security researchers found in the files masquerading under that name: