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What is a Computer Virus? Definition, History, Types, Symptoms

  • Last Updated : 17 Aug, 2021
Geek Week

A computer virus is a sort of malware that attaches itself to another program and can replicate and propagate once it has been installed on a user’s computer. When a computer changes the way in which it should work normally, it is said to be infected by a virus. This virus may spread from one computer to another. For example, you may receive an email with a harmful attachment, inadvertently open the file, and the computer virus then infects your machine. Or in other words, a harmful software application that is installed without the user’s knowledge/ consent on their computer and then performs some malicious acts is known as a virus. A virus attaches itself to another software, once infected the system, in such a way that the host program’s execution activates the virus’s actions simultaneously. It has the ability to self-replicate itself into other programs or files and infecting them. Computer viruses are harmful but the majority of them engage in malicious activity, such as data destruction.

History of Computer Virus:

Viruses have been infecting various devices for a long term via the Internet or some other medium. The viruses are created with an intention to steal information, completely destroy the device, etc. The “Creeper system, ” the first computer virus, was an experimental self-Multiplying virus launched in 1971. Then, the Rabbit virus came in the mid-1970s and was extremely active and it self-replicated very fast & wrecked the functionality at the same speed. The first PC virus was known as “Elk Cloner” and was built in 1982, by Rich Skrenta. It spread by a floppy disc with a game on it and hooked itself to the Apple II operating system.
“Brain,” the first computer virus for MS-DOS, was introduced in 1986. The boot sector of the floppy disc would be overwritten, preventing the computer from booting. It was created by two Pakistani brothers and was intended to be used as a copy protection system. In 1988, the age of catastrophic viruses began. Most viruses were basically joked with humorous names and messages till then. In 1988, “The Morris” was the first virus that propagated widely.

Types of computer virus

  • Boot sector virus: This virus infects the boot sector of the computer and runs every time the computer boots and before the operating system loads. Floppy discs and other bootable media become infected. They are sometimes referred to as memory viruses because they do not infect the file system.
  • File Virus: Infects the system by appending itself to the end of a file. It changes the start of a program such that the control jumps to its code.
  • Email-Virus: They are comprised of malicious code that is propagated through email messages and can be activated when a user clicks on a link in an email message, opens an email attachment, or interacts in any manner with the infected email message.
  • Polymorphic Virus: Poly means many and morphic means forms. So this virus changes its form every time. A virus signature is a pattern that can be used to assess whether a virus exists or not (a series of bytes that make up virus code). This virus changes itself every time when it is installed so that it can avoid detection by antivirus software. Here, only the signature of this virus is updated, the functionality remains the same. 
  • Macro Virus: These viruses are activated when a program capable of performing a macro is executed. Macro viruses, for example, can be found in spreadsheet files.
  • Multipartite Virus: This virus has the power to infect a computer’s boot sector, memory, and files, among other areas. This complicates its detection and containment.
  • Encrypted Virus: To avoid detection by antivirus software, this type of virus is encrypted. There’s also a decryption algorithm included. As a result, before running, the virus decrypts.
  • Stealth Virus: This virus is difficult to detect because it modifies the code used to detect it. As a result, virus detection is extremely difficult.
  • Resident Virus: A virus that saves itself in the computer’s memory before infecting additional files and programs after the original software stops working. Because it is hidden in the computer memory and difficult to remove, this virus can easily infect other files.
  • Direct action Virus: If a virus is tied to an executable file and when the file is opened or run, that virus gets installed/ spread, it is known as “direct action”. This virus does not delete any files or lay impact on the speed of the system; it just renders your files inaccessible.

What does a computer virus do?

A virus can harm or destroy data, slow down system resources, and log keystrokes, among other things. A virus has the ability to have unexpected or harmful outcomes during this procedure, such as destroying system software by corrupting data. Some computer viruses are designed to damage your computer by destroying files, corrupting applications, or reformatting the hard drive. Even less dangerous computer infections can have a substantial impact on your system’s performance, eating up RAM and triggering frequent crashes. Other viruses may just clone themselves or flood a network with traffic, rendering all internet activity difficult. 

How a computer gets a virus?

Through the following activities you may get your device infected by the virus :



  • Sharing the data like music, files, and images with each other.
  • If you open a spam email or an attachment in an email that is sent by an unknown person.
  • Downloading the free games, toolbars, media players, etc.
  • Visiting a malicious website.
  • Installing pirated software(s) etc.

Symptoms of a computer virus?

If your system is infected by the virus, the following symptoms may be seen :

  • Opening of Pop-up window frequently: Pop-ups may entice you to visit odd locations. They will take you to a page to download any antivirus (which is actually not an antivirus), or other harmful software.
  • Slowing down of system without any reason.
  • Updated homepage: For example, the homepage is replaced by a website and you would not be able to undo that replacement.
  • Identifying that your files are corrupted.
  • Change in the name of your hard drive & also change in its volume.
  • Change in amount of free memory available.
  • Not able to find your files or programs.
  • Unknown change in the password that does not let you login.
  • A virus may damage your hard drive and our device may freeze or crash as a result of this.

How to remove computer viruses?

To get rid of a computer infection, you have two options:

  • Do-it-yourself manual approach
  • Seek the assistance of a reliable antivirus product.

In the manual approach, online search is usually the first step in this approach. You can be requested to complete a huge list of tasks. To finish the procedure, you’ll need time and maybe some experience.

The simpler approach is to install antivirus. Antivirus software is a program that searches for, detects, prevents, and removes software infections that can harm your computer. Antivirus can also detect and remove other dangerous software such as worms, adware, and other dangers. This software is intended to be used as a preventative measure against cyber dangers, keeping them from entering your computer and causing problems. Antivirus is available for free as well. Anti-virus software that is available for free only provides limited virus protection, whereas premium anti-virus software offers more effective security. For example Avast, Kaspersky, etc.

Sample Question

Question 1. How can you protect your computer system from viruses?

Solution:

We can use antivirus software to keep your computer safe from viruses. Antivirus software works by comparing the files and programs on your computer to a database of known malware types. It will also monitor computers for the presence of new or undiscovered malware threats, as hackers are constantly generating and propagating new viruses. 

Question 2. Make a list of frequent computer virus infection sources. 



Solution:

The sources via which you can infect your system with viruses are :
1. Downloading programs/software from the internet.
2. Emails
3. External devices like pen-drives
4. Using an unknown CD to Boot data
5. Bluetooth/ infrared

Question 3. Why is it a good idea to back up data on a regular basis?

Solution:

Files that have been damaged can be restored by backup.

Question 4. How do computer viruses spread?

Solution:

Computer viruses are typically propagated by email, file sharing, or CDs or by downloading file(s) from unauthenticated sources. 

Question 5. What is a computer virus?

Solution:

It is a harmful software application that is installed without the user’s knowledge/ consent on their computer and then performs some malicious acts, is known as a virus. It attaches itself to another software, once infected the system, in such a way that the host program’s execution activates the virus’s actions simultaneously.

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