I need a custom user registration script (PHP,MySQL) that is totally modular, i.e. completely independent of any graphical front end. Robustness, security, and scalability are paramount. The email verification paradigm is a minimum requirement.
The script will be tested, and by tested I mean assaulted and nitpicked with a fine-tooth comb. Please, don't submit any of the free scripts accessible from the web as we have seen them all.