index.php to prevent unwanted access?

If I put a blank index.php or index.html file in all my serverside directories, will that prevent bots from seeing what else is there? I.e., does the presence of index.php or index.html prevent someone from getting a directory listing? If they can't get a directory listing, then surely they can't see what I don't want to them to see?

Add Options -Indexes into your .htaccess file to prevent directory listing.

thanks, I'll try that out!