There are plenty of ways of securing the download, download guard or dropbox etc but if somebody actually uploads your product to a blackhat site there isn't really a lot you can do about it.
The best tip I've come across is to make sure there is an offer at the front of the book that goes to your squeeze page. I have heard of somebody who picked up a $1000 a month client from a pirated book.
Realistically if somebody downloads your book from a blackhat site it's unlikely that they would ever have purchased it anyway. The way to look at it is that it showcases your products to an audience that you probably would never have reached otherwise, and if you can get some of them onto your list then that's a benefit.
Illegal sharing isn't going to impact your sales to any great extent and simply is just a fact of life on the internet. Don't worry about it.