Get the Whitepaper called Web Backdoors – Attack, Evasion and Detection. This paper provides insight on common web back doors and how simple manipulations could make them undetectable by AV and other security suits. It explains a few techniques that could be used to render undetectable and unnoticed backdoors inside web applications.
You can download it from the following link: https://packetstormsecurity.com/files/download/107541/web_backdoors_evasion_detection.pdf
Source: https://packetstormsecurity.com/files/107541/Web-Backdoors-Attack-Evasion-And-Detection.html