Where to keep digital products from thieves

Hi everyone,
I have a few websites with digital products for sale. I sell it with PayPal buttons. I tried to keep files with them in two different ways:
1. Eliminate from site map (and keep as txt robot files like this okgjlkjfoh.html)
2. Keep on site map (okgjlkjfoh.html) and eliminate from txt robot files
The math is next:
1 person buy & 7 steal!
Is this program can help me? How?
If somebody has any fresh idea, please share it with me and other people.
Thank you in advance

yes, this program can help you by making your files inaccessible to non-customers.

amember user htaccess protection to prevent "hotlinking".

David