Restricted access

From Joomla! Documentation

Most PHP files within Joomla! begin with the following statement:

defined( '_JEXEC' ) or die( 'Restricted access' );

This statement checks to see if the file is being called from within a Joomla! session. This protects your site by making it more difficult for a cracker/hacker to damage your site.

However, this line should NOT be included in your main index.php file, since this is the program that starts the Joomla! session.