Here we are reading your sites, needing to sell how-to movies and training programs. It looks like ClickBank will send the download to the buyer’s email address but what stops the buyer from burning the movie to disk or sending it on to others we do not know, or selling it as their own?
You are right. ClickBank will handle credit card payments and digital distribution, but does not address the issue of piracy. The type of security you are asking about is called Digital Rights Management (DRM.)
The benefit of DRM is obvious: only those who pay for your content will be able to open it. But the downside is increased support costs for you, and increased aggrevation for your buyers.
If you want to explore what is available in DRM for small publishers, here are a few links: