Some web hosting server setting allow the directory listing by default and you wish to disable it as you might not use the hosting space for web purpose but storage purpose.
There are several ways to disable it through your space as steps below.
Apache Linux with cPanel
If your hosting company provide cPanel, it will be great it allow you easily to disable it through the control panel.
In this guide, Mick Genie guide you how to disable it through cPanel 11.25(x3 themes).
1. Log into the cPanel control panel.
2. Look for Advance box and click on Index Manager.
3. A pop up box show and select the domain name that you wish to disable it.
4. Select the folder.
5. From the radio button, select No Indexing and save it.
Apache Linux without cPanel
If you do not come with cPanel, it isn’t a hard step to disable it.
1. Log into the SSH console.
2. Change directory to the public_html path(assume your root path is /home/mickgenie/public_html/)
3. Edit/create the .htaccess file
4. Add the line as below to the .htaccess file by click on Insert button and insert,
5. Save it by type in :wq!.