If you are looking for files for the original 2011 MW3 (often for the Plutonium mod), there are legal ways to acquire them:

For an explanation of how the game's file structure has changed recently with the removal of MW3 from the 'COD HQ' launcher:

Modern Warfare 3 organizes its data assets into stored inside the zone folder of your game directory. The game separates these files by language and game mode.

Signs of corruption include:

: The game freezes on the map loading screen because it cannot access the underlying asset package.

Modifying game directories with files sourced from unauthorized third parties can trigger Team Ricochet—Call of Duty's anti-cheat system. This frequently results in permanent hardware or account bans. How to Properly Restore Missing MW3 Zone Files for Free

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Right-click on and select Properties . Go to the Installed Files tab on the left menu. Click the Verify integrity of game files button.