Incapsula Backdoor Protection is free for existing and new customers. Backdoor protection is based on signature-based detection and live traffic monitoring. Backdoors can be used to distribute spam and malware, launch distributed denial of service (DDoS) attacks, or to help steal valuable data like credit card numbers like those of the U.S. banks who were attacked by the ‘Zombie Bot army’ Backdoor is a function that enables hackers to remotely operate a site or server, even after whatever exploit they used for initial access has been patched.
Source: https://thehackernews.com/2013/01/incapsula-introduces-backdoor-protect.html