When a web browser is pointed to a directory on your website which does not have an index.html file in it, the files in that directory can be listed on a web page. To have the web server produce a list of files for such directories, use the below line in your .htaccess (can be found in FTP -> public_html folder):
To have an error (403 – Forbidden) returned instead, use this line:
It is important to prevent access to files in your folder when the folder doesn’t have an index files for security reasons. This is highly recommended.