Keith Casey has a suggestion for budding (PHP) developers out there looking to jump head first into their first project: "Don't trust the users."

Recently I taught a class of bright-eyed, bushy-tailed PHP'ers just getting their start in the world. They haven't done their first production application and we were working in the "safe" confines of a classroom, but there was one concept that I pounded into their heads: Don't Trust the Users.

Generally, as Keith mentions, users aren't malicious/incompetent/ignorant 99 percent of the time, but there's always that off chance that they are and you need to protect you and your application from it by filtering input and escaping all output to prevent any mishaps.