Check and close all backdoors to a script. (Legally licensed to me)

Hi, I bought a script from a website and can show you proof of ownership with a valid license. The issue I have with the script is the developers have put a lot of backdoors into the script in which they can control my site. This makes me extremely uncomfortable. I want a programmer to go through the code and block all backdoors so they have no control over my site. I will also need every back door they have to be documented so I can confront them on the matter. The script is a php / mysql script. Contact me via PM for details. Thank you