File Access & Security Issues

How assured can I be that people will NOT be able to view my php code? I'm creating an e-commerce site that will contain sensitive information and algorithms. I want to to take every precaution possible to protect that data and code. One concern in particular is the ability to view the contents of a file through PHP, rather than through HTTP. I've noticed that many file functions do not work for non-local files, which is good. But can a good hacker still get access some indirect way? Thank you! Steven J. Walker Walker Effects www.walkereffects.com steve@walkereffects.com