This file contains a list of important system files that are to be checked each day by the system security check script /etc/security. Each file is listed by full path, on its own line. Every day, these files are backed up into /var/backup and compared to the version of the file that existed yesterday. Any changes to these files are mailed to root. Feel free to add any files you like to this list.
For more details on how the security check works, see /etc/security.