If your host allows overrides in the .htaccess file, you can add this to the root .htaccess file to prevent directory browsing (and indexing by search engines):
Options -Indexes
Add that right to the top of your root .htaccess file (located in the same location as wp-config.php and readme.html normally).
It’s also possible your host’s control panel has an option to turn off directory browsing. You could use that instead if it’s easier.
Then try accessing the folder with a browser to see if you can get a directory listing.
Thanks very much for the swift reply chrishajer. I’m going to see if I can disable directory browsing on my server first.
I’m guessing none of the suggestions you gave me will affect normal indexing of the WP website?