Someone can browse your folder directly by writing folder names such as images, js, and CSS along with URL and steal all files from that folder. If you enter the image folder name with URL Link, it will browse all the files inside that folder.
Above example, anyone can browse entire images on image folders.
How to direct access directory and make a secure site?
1. Create a .htaccess file on the website root directory and paste the following code in your .htaccess file.
# directory browsing Options All -Indexes