Because I have been asked, I will put up the source code (for the batch file) and explain each command and what it does. Be Aware! This is the current...
This instructable shows you how to create a backdoor on a computer with netcat! I will show you two ways to do this, with and without my batch file that automates it for you. This instructable already assumes that you have already got root permissions on the computer, probably with a 0phcrack LiveCD here. Now, onto the instructable.
I have saved you the trouble of 3 minutes of searching Google and have put nc.exe up on instructables for you to download. Optionally, you can also download nc.bat which is a batch file I have created to automate the process for you. Make sure that if you download nc.bat it is 464 bytes, because I kept on uploading versions and finding out something was wrong with it. If it is not 464 bytes, the program will not correspond with this instructable.
First, both files must be in the same directory for nc.bat to work properly. I suggest using a flash drive, or CD-ROM for this operation. I used a 512 mb geek squad flash drive for this, but that is just me. So, copy the files onto your external media device, and bring them to the computer that you have root on. Get on the media device and double-click nc.bat. This will copy the nc.exe file to the system32 folder, in the system root (usually C:\Windows or C:\WINNT) and make the necessary changes to the registry. Then write down the IP address. It will be something like '192.168.1.103', which is mine. Once this is done, reboot the machine and login. Then the anti-virus program may ask you if you want to allow/disallow the program. Click on 'Allow' or similar. Keep in mind that in this instructable, you can only telnet in from the local network of that computer. Then leave, or log off, or whatever else you want.