Originally Posted by Purple Lady
I downloaded my purchases again after my credit card was stolen because at some point in the future I won't still have the data that I provided to make the purchase. I can't keep track of different credit cards used to make purchases. I do disinfect when I get my books, but if at some point in the future something happens to my Calibre library and I have to disinfect again it's easier to have all my books with the same credit card.
As far as I know, the book is encrypted when you download, not when you purchase. If you change your credit card info on your account and redownload, the books will still work.