Digital products - are downloadable items secure?

Hi all!

I'm just starting to explore Marketpress and have a question about downloadable products. As far as I can see, by using the "File Upload" button in the "Product Download" section of any product page, the file location doesn't seem to be protected in any way. It looks like the sample below:

http://example.com/teststore1/files/2012/01/product.pdf

Therefore, anyone who knows the url can download by copying it to their browser's address bar and bypass the payment step. I've tried it and was able to access the downloadable file with no problem.

I may be missing something obvious here but, is there a way to secure the file location?

Any help is appreciated.