New on DevShed.com today is a tutorial helping you optimize your file downloading for your web application and provide a way to give users dynamic links to files instead of direct ones.
The true path to the downloadable content can be revealed easily and is not protected, allowing users to bypass web forms and download the content directly using a browser. [...] The Solution: A Secure and Efficient PHP Download Script
This tutorial is actually an update of their previous tutorial looking at a similar subject, with a few differences. Their code provides a way to limit the files a user can download, the number of times they can download it and a script to read the file and push it to the user without them ever knowing the path.