A. System File Checker replaces corrupt or missing protected files and refreshes corrupt or missing DLL cache components with the latest files from the installation media, service packs, or hotfix/patch locations, whichever was registered most recently. Because System File Checker overwrites existing hotfixes and patches, you have to reapply them after you run the

sfc /scannow 

command. Microsoft has corrected this behavior in all Win2K Service Pack 4 (SP4) and later hotfixes and patches, which now register themselves in such a way that System File Checker can "see" them during file-restoration operations.