And if you mean that people can see a list of the files in the directory, then you should copy, or link, or just rename your login php page to index.php. When one types the url with just a directory, and no specific file, Apache will default to index.html, or index.php; or if neither of those exists, it will show the list of files in the directory.
 You may have to edit httpd.conf to include 'index.php'. Look for the section like this:
And make it look like this:
DirectoryIndex index.html index.php
You should also add an index.html to all subdirectories, which will redirect requests to your login page. [/edit]