In Microsoft® Windows® XP, Windows File Protection prevents the replacement of protected system files such as .sys, .dll, .ocx, .ttf, .fon, and .exe files. Windows File Protection runs in the background and protects all files installed by the Windows Setup program.

If a program attempts to replace or move a protected system file, Windows File Protection checks the file's digital signature to determine if the new file is the correct Microsoft version. If the file is not the correct version, Windows File Protection either replaces the file from the backup stored in the Dllcache folder or from the Windows CD. If Windows File Protection cannot locate the appropriate file, it prompts you for the location.