The only thing truly unbreakable is a program called StrongBox.
To this date it has never been broken. They guarentee it's 100% unbreakable or your money back!
The guy who built it can't even crack it and he's got 20 years programming experience and 6 years on linux!!!
We use it on all our paysites and we have never been compromised, we will never use anything but strongbox. It's affordable, reliable and the programmer Ray, is a great guy!
You can take a look here
http://webmastersguide.com/ and just hit the "Strong box" link.
Have a good one!