Use the saber to create your own simple back door[has been issued with the hacker X-Files]-vulnerability warning-the black bar safety net

We all know nc is a powerful and flexible hacking tools, he can do many things, such as a telnet client port, such as the invasion of time to bounce back the shell, such as scanning...... But have you ever wondered will he build into a service-level Backdoor? Now much better with me as the rookie...