Previous versions of Windows would allow software installations to replace your operating systems files.
Windows 2000 File Protection, WFP, uses file signatures to manage the %Systemroot%\System32\Dllcache folder.
When a file is changed, a background task determines wether it is a protected file, and wether the new file has the correct Microsoft version. If not, the file is replaced from the Dllcache, if present. An Administrator would see:
A file replacement was attempted on the protected system file name. To maintain system stability, the file has been restored to the correct Microsoft version. If problems occur with your application, please contact the application vendor for support.
All SYS, DLL, EXE, TTF, FON, and OCX files included on the Windows 2000 CD-ROM are protected, but not necessarily in the Dllcache.
If a file that needs to be restored is not in the Dllcache, WFP asks for the installation media.
See tip 2075 for more information.