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Computer Virus

What is Computer Virus?

A computer virus is a computer program that can copy itself and infect a computer without permission or knowledge of the user. These programs are destructive to computers. Any computer program that can cause damage to a computer is called malicious software. The computer viruses can damage or corrupt data, modify existing data, or degrade the performance of a system by utilizing resources such as memory or disk space. The computer viruses are broadly classified into the following categories:

  • Worms
  • Trojan
  • Boot sector virus
  • Master Boot Record (MBR) virus
  • File infector virus
  • Macro virus

Computer Virus


Worms

A computer worm is malicious software that spread from computer to computer without the use of any host files. Therefore the worms are spread through networks like LAN, WAN, and also through the Internet and there are various ways by which a worm spread through the Internet like E-mails, Messaging, and Chats.

  • Blaster
  • Code Red
  • Fog
  • ILOVEYOU
  • WANK
  • Witty

Worms


Trojans

A computer Trojan simply called Trojan is another type of malicious software that appears to perform a certain action but in fact, performs another and often these hidden actions are for negative purpose only like:

  • Retrieving a user’s account name and password without the user’s knowledge to gain remote access.
  • Spreading other malware, such as viruses: this type of Trojan horse is called a 'dropper' or 'vector'.
  • Erasing or overwriting data on a computer.

Spying on a user to gather information like browsing habits of the user, etc. These types of programs are called spyware.

Some examples of computer Trojans are:

  • AIDS
  • Beast Trojan
  • Bifrost
  • Nuclear RAT (NR, NucRat)
  • Insurrection
  • Bandook
  • Optix Pro
  • Shark

Trojans

Boot Sector Virus

A boot sector affects the boot sector of an infected computer. A boot sector virus is spread through infected floppy disks.

The boot sector virus can harm a computer in a variety of ways. Therefore the most visible effect of a boot sector virus-infected computer is that it prevents the computer from booting. When you try to start the computer, you will get the error message "Invalid system disk" quite prevalently. A boot sector virus can also make data disappear from entire partitions.

Some examples of boot sector viruses are:

  • Form
  • Disk Killer
  • Michelangelo
  • Stoned


Boot Sector Virus

Master Boot Record (MBR) Virus

An MBR virus is very similar to the boot sector virus, in both its functioning and source. However, unlike the boot sector virus, an MBR virus affects the master boot record of a computer. The MBR viruses are activated when the BIOS activates the master boot code before the operating system is load and the impact of an MBR virus is almost the same as that of a boot sector virus. Some examples of MBR viruses are

  • AntiEXE
  • Unashamed
  • NYB

Master Boot Record (MBR) Virus

File Infector Virus

A file infector virus infects the ordinary program files on a disk. When you run a program infected with a file infector virus, the virus infects the other executable programs on the computer. The Files that are usually infected by a file infector virus are the EXE, COM, SYS, or BAT files. A file infector is usually spread to other computers by sharing the infected files.

Some examples of File Infector viruses are:

  • Snow.A
  • Jerusalem
  • Cascade

File Infector Virus

Macro Virus

A macro virus is a kind of virus that is written using the macro feature of an application. The macro feature is available only in certain applications like MS-Word, MS-Excel, MS-PowerPoint, MS-Access, Corel Draw, etc. When a document infect by a macro virus is open, the virus copies itself to the default document template.

  • Concept
  • Nimda
  • Melissa

Macro Virus

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