Selling digital books is substantially different from selling printed books or other products.
Customers expect to get the book in a very short time as there is no shippment required. The copyright owner would like the paying customer to be able to read the book however he/she would not like the customer to be able to copy the file and distribute it.
This is exactly what you get with EPUBCLOUD along with HBreader reading application.
This is a full package that gives you copy protection for a very low price, while maintaining ease of use for the end customer.