If that folder lacks an index.html file, Google will find the directory list, index the full URLs of your MP4s, and potentially show them in search results. Suddenly, your $200 premium course is accessible via a direct link on Google.
Here is a table of ready-to-use dorks. Remember to replace the series or movie name with your own search term. google index of series parent directory
This removes generic server default pages and forum structures. If that folder lacks an index