The nice thing about the Internet is that anyone can access your web site. This can also be a drawback. PHP (and the other components of LAMP) make it very easy to produce afunctional, useful website.
Of course, "easy" and "secure" are orthogonal concepts.
If you care about your data or your customers' data, you need to think about security. How can you keep out the bad guys? How can you prevent and, if needed, recover from errors? How will you know if things are working correctly or if someone is snooping around in the dark corners of your site?
This collection of articles from the PHP Dev Center on ONLamp.com answer these questions and more. John Coggeshall, the PHP Foundations columnist, explores the techniques crackers might use to exploit your site and demonstrates not only how to thwart those attacks but how to think to preventatively. Clancy Malcolm, an experienced open source consultant and developer, presents ten practical techniques to make sure your code and sites are secure.
Security is a process and, unfortunately, often a race through dark places. You don't know who's out there and what they know. You can, however, be confident that you've minimized your risks. This collection will help.