What is a Computer Virus? Definition of Computer Virus?

What is a Computer Virus? Definition of Computer Virus?

A computer virus is a malicious piece of code or program that embed itself in a file and executable program, it activates on running the file or clicking the attachment, it has the ability to replicate itself and it spread from one computer to other via an infected device, email attachment or network.

How virus works? Types of the Computer Virus? Function of a Computer Virus?

According to working and function virus have different types

Types of virus:

Boot sector virus: This type of virus was common when floppy disks were used to boot the computer. This type of virus obsolete but still exist and it run its operation in computer when you start it. This virus is tied to the boot menu.

Browser Hijacker: When you enter a URL of a website but your browser will bring you another website, then web browser is infected with this virus. This virus usually attached appealing toolbars and other free downloads. Many trusted browsers built in feathers are available to prevent or block this virus.

Web Scripting virus: Some malicious websites keep the malicious code with the code of video, links, ads, and images. When users click them, it automatically download or direct you another malicious website.

Overwrite Virus: This virus overwrites the content of a file and original content lost, it can infect the files, folders as well. To get rid from this virus, you should get rid of your file. So always keep back up of your data.

Resident Virus: After entering in the computer, it resides inside the RAM of the computer and interferes with the normal working of the computer. It damages and corrupt the files and very difficult to detect and remove. It infects both executable file and boot sector. It works with operating system and after damaging the files it clear up space its own.

Polymorphic virus: It is very difficult to detect this virus with ordinary antivirus because it has special method of encoding or encryption every time they infect a system.  Polymorphic virus changes its code every time when infected file is executed.

Macro Virus: Micro virus hits that files made from program and application that support macro like MS Word. People unknowingly download it with email attachment, it not only infect the user but also send email copy of infected file to the contact list.

Multipartite virus: This virus spreads in several ways, so it is very frustrating to remove this virus. This effects both executable and boot sector files. It action depends upon type of operating system, certain program and files.

File infector virus: File infector virus mostly attached with .exe or .com files. When user runs these files this virus activates it take over the file slow down the program.

Space filler virus: Instead of attaching its self to code and increase file size; it tries to get into the empty space inside the file that’s why it is called “cavity virus”.

Why virus is used? Why virus harmful?

  • Virus is designed for malicious and damaging purposes.
  • It slows down the system performance.
  • Virus damages or deleted the files and operating systems.
  • Hackers use them to steal the private information of the people like credit card and other private detail.
  • Web browser hijack and leads to other sites and show abnormal behavior.
  • Program opens and runs without the knowledge and intervention of the user.
  • System performance slows down, freezes or crashed.
  • Unknown icon appears on the desk tops.
  • Important files miss or delete automatically.
  • During running of system unusual sound comes, pictures and ads pop up and programs terminate unexpectedly.
  • Operating system displays warning messages frequently.
  • The email sends to contact list without the user permission.
  • Most important unauthorized access to system and network resources.
  • Files are over write and contents are lost.
  • Virus affects the hard ware performance.
  • Warning of fire walls display.

History of Computer Virus? Timeline of Computer Virus?

Theory of Self Replicating Automata: The concept of computer program that replicates itself first discussed by mathematician John von Neumann in the late 1940s and it published in 1966.

In 1971 the first worm program was written by Bob Thomas is called “creeper”. It was an experimental program written to prove the “Theory of self-reproducing automata” of John von Neumann’s.  Creeper got access through ARPANET and infected DEC PDP-10 computers running the TENEX operating system and displayed the message “I’m the creeper, catch me if you can!”.

The Rabbit virus: It is called Rabbit virus because of its speed of replicating itself. It was developed with malicious intent in 1974. This infectious virus made several copies of itself when you on Computer and slow down the performance of the computer.

The “Brain” the first boot sector virus developed by two Pakistani brothers Basit and Amjad Farooq Alvi in 1986 that ran a computer store. It infected the boot sector of floppy disk and replaced it with its own code. They made this virus to prevent the illegal use of their software.

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