Only One Digital Download Per Buyer

I have a website and people can buy and download this digital ebook. I only want them to be able to download the ebook one time (per buyer). How do I go about doing this? Here is my website if you need it: http://www.quitting-smokingnow.com Thanks!!

You would do this with a database and a server-side script (most likely PHP). Ask a moderator to move your question to the PHP forum for better assistance.