Why should there be an index.html in all my directories?

All directories, which should not be accessed directly via an URL, should hold an index.html with HTML code to return the visitor to the previous page.

If this is not done, there is a possibility that the directory content (the files) will be listed and potentially opening up for misuse of e.g. images, files for download or script files that are not intended to be accessed directly.

This Q&A was found on XOOPS Web Application System : https://xoops.org/modules/smartfaq/faq.php?faqid=187