Parent Directory

I was given the management of a website due to the loss of the webmaster and was given the following problem from a user:

When I go to a web page (I'll use generic titles) as such: www.aaa.bbbbbb.ccc/dddddd/intro.htm - everthing is fine. However if you backspace out the intro.htm (www.aaa.bbbbbb.ccc/dddddd) then you receive the following page:

Index of /dddddd

Name Last modified Size Description

Parent Directory

and then a listing of all the files in that directory.

How do I turn that feature off so it gives me a Forbidden Access page.