Critical files, Let say configuration.php file for Joomla
1. Make a backup copy of your .htaccess file. Use your backup file to recover if the following fails. Be sure to delete the backup file once you are finished.
2. Add the following to your .htaccess file. This example will protect the configurtation.php file.
<filesMatch "configuration.php"> Order allow,deny Deny from all </filesMatch>