I hate to look down my nose at other programmers, because I understand that we all start somewhere, but if you are building a financial exchange and you encrypted passwords using unsalted MD5 at any point in the history of your product, you have proven to me that you are learning as you go, and there is no way in hell I'd trust you with any significant sum of money.
Edit: Note, this really barely scratches the surface for building secure software. AC says how to apply cryptographic primitives correctly. It won't teach you how to avoid vulnerabilities specific to particular application domains (like CSS, SQL injection, etc...).
That book is old, and though still basically correct, there's much better ways to learn about the practice of developing secure systems. I recommend "Cryptography Engineering" by Ferguson, Schneier, Kohno which is a more modern descendant of Schneier's AC.
Being a programmer means committing yourself to a life of continued education. Building a secure authentication system? Time to read up on the subject. You don't have to go far before you learn about the vulnerability of MD5 hashes for password storage.
