Hi,
I am facing a very big problem, if someone types the directory name into the browser, a full listing of all the files in that directory is shown. This could be a security risk for my site.

This is because, you don’t have no index file in your directory. To prevent this either you create a index page or if you don’t want to create lot of index files, then, you can enter a command into your .htaccess file to stop the directory list from being shown:

Options -Indexes