backdoor is a hidden piece of code, script, or a program placed on a system for persistence purposes, so you don’t have to exploit the same system twice. It simply gives you quicker and instant access to the system.

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• SSH Backdoor
• PHP Backdoor
• CronJob Backdoor
• .bashrc Backdoor
• pam_unix.so Backdoor
• Backdoor as a Service “Systemd”
• sources