Effect of Computer Virus

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Different Types of Computer Viruses
Computer virus is a software program written with malicious intentions. There are number of computer viruses that can impede the functioning of your computer system. Let us find out the different types of computer viruses. Did You Know?

In 2010, Stuxnet virus targeted Siemens Industrial Software and Equipment. There are allegations that this virus is a part of a U.S. and Israeli intelligence operation named "Operation Olympic Games" and it hit Iran's nuclear plant Natanz.

Computer virus is a harmful software program written intentionally to enter a computer without the user's permission or knowledge. It has the ability to replicate itself, thus continuing to spread. Some viruses do little but replicate, while others can cause severe harm or adversely affect the program and performance of the system. A virus should never be assumed harmless and left on a system.

There are different types of viruses which can be classified according to their origin, techniques, types of files they infect, where they hide, the kind of damage they cause, the type of operating system, or platform they attack. Let us have a look at few of them.

Memory Resident Virus

These viruses fix themselves in the computer memory and get activated whenever the OS runs and infects all the files that are then opened.

Hideout: This type of virus hides in the RAM and stays there even after the malicious code is executed. It gets control over the system memory and allocate memory blocks through which it runs its own code, and executes the code when any function is executed. Target: It can corrupt files and programs that are opened, closed, copied, renamed, etc. Examples: Randex, CMJ, Meve, and MrKlunky

Protection: Install an antivirus program.

Direct Action Viruses

The main purpose of this virus is to replicate and take action when it is executed. When a specific condition is met, the virus will go into action and infect files in the directory or folder that are specified in the AUTOEXEC.BAT file path. This batch file is always located in the root directory of the hard disk and carries out certain operations when the computer is booted.

FindFirst/FindNext technique is used where the code selects a few files as its victims. It also infects the external devices like pen drives or hard disks by copying itself on them.

Hideout: The viruses keep changing their location into new files whenever the code is executed, but are generally found in the hard disk's root directory. Target: It can corrupt files. Basically, it is a file-infecter virus. Examples: Vienna virus

Protection: Install an antivirus scanner. However, this type of virus has minimal effect on the computer's performance.

Overwrite Viruses

A virus of this kind is characterized by the fact that it deletes the information contained in the files that it infects, rendering them partially or totally useless once they have been infected.

Hideout: The virus replaces the file content. However, it does not change the file size. Examples: Way, Trj.Reboot, Trivial.88.D
Protection: The only way to clean a file infected by an overwrite virus is to delete the file completely, thus losing the original content.

However, it is very easy to detect this type of virus, as the original program becomes useless.

Boot Sector Virus

This type of virus affects the boot sector of a hard disk. This is a crucial part of the disk, in which information of the disk itself is stored along with a program that makes it possible to boot (start) the computer from the disk. This type of virus is also called Master Boot Sector Virus or Master Boot Record Virus.

Hideout: It hides in the memory until DOS accesses the floppy disk, and whichever boot data is accessed, the virus infects it. Examples: Polyboot.B, AntiEXE
Protection: The best way of avoiding boot sector viruses is to ensure that floppy disks are write-protected. Also, never start your computer with an...
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