Among the files and directories to be protected are those that make up the operating system software itself. The standard set of permissions on system files and directories provide a reasonable degree of security without interfering with the computer�s usability. For high-level security installations, however, you might want to additionally set directory permissions to all subdirectories and existing files, as shown in the following list, immediately after Windows NT is installed. Be sure to apply permissions to parent directories before applying permissions to subdirectories.