To test your website for vulnerabilities

Good afternoon, you must test in-house website for vulnerabilities and the possibility of hacking.

The situation is following someone through the form as it came to hosting and executed the PHP code, I need to know how he did it!!!

The site is written by me, source code available (you just need to understand what you need to protect).

Site on pure PHP 5 is the application form for Ajax

Code, Ajax form and a php file to accept data from this form will provide.

Offer price and terms.