Southern writes:  

With DisposableLinks, a PHP script package, you can easily create secure 'throw away' download links for the delivery of your digital goods. DisposableLinks links can be set to expire after a certain amount of clicks, or after a specific amount of time, and can also be locked to a specific IP, which means that even if someone shares a link before it has expired, it will not work for anybody else. Additionally you can disallow downloads from specific countries. And: you can even embed customer data dynamically into any downloaded file!

DisposableLinks