A lot of times, when you have a web server, you need to prevent Indexes to be
shown.
I ran into that problem the other day and although some Virtual Hosts accepted
the following for not showing indexes, others wouldn't:
<Directory /path/to/web>
Options -Indexes
</Directory>
This approach would remove the ability to have Indexes shown accross all your
Virtual Hosts, with code:
sudo a2dismod autoindex
sudo apache2ctl graceful
The first command just disables the module and the second restarts Apache in a
graceful mode (will keep connections alive).