When a website is compromised, attackers frequently leave behind a backdoor – according to our research around 70% of all website hacks include a backdoor. These backdoors are not designed to attack a website or destroy data, instead they allow an attacker to re-enter a targeted website with little to no authentication, providing them with unauthorized access to the system.
Backdoors can be planted anywhere within a site, file system, or database.
Story added 15. September 2017, content source with full text you can find at link above.