I've had first hand experience with this issue after the production of my ebook, The Webmasters Book of Secrets. Initially I was using PayPal as a payment method. After users purchased the book, they were shown a Thank You page where they could download the ebook. I soon discovered that users could find the Than You page URL in the PayPal code, bypassing the purchase process.

After discovering the issue I moved quickly to better understand how to properly protect my digital assets. I found software programs that allowed me to protect a digital library but didn't like the fact that they required the download of an executable file. I feel like executable files are risky for buyers and may be seen as having an ulterior motive.

By the end of my search, I determined that the best way to protect my download was with the help of ClickBank. I'm sure there are other marketplace related selling tools out there, but ClickBank was able to provide me the protection I needed at relatively low cost. The result is that when individuals buy my ebook, they are buying it through the ClickBank marketplace. This marketplace provides encrypted protection and does not display the confirmation URL (which includes the download link).

Once you've found a distributor that provides the protection you need, you should also consider protection your Thank You pages. Be sure to use the Nofollow command in your meta tags on each Thank You page. An example of this is: META name="robots" content="noindex, nofollow". Using this tag signals the search engines to not index your page. Doing so eliminates the possibility that someone will be able to find your page when searching the web.

You've worked hard to create your product, make sure to protect it!