What is a Computer Virus and types of Virus?

What is a computer virus?

We all must have heard of the term virus, even many of you have also had an attack of viruses on our body or might have suffered from viral fever, which may have left you weak. Unlike biological viruses attack our body system, computer viruses attack a computer system.

Hence, “A virus is a computer program or software that enters the computer system by attaching itself to another computer program and spreads itself across the system.

In more technical terms, a computer virus is a type of malicious code or program written. The term virus stands for ‘Vital Information Recourse Under Siege.’ Viruses spread from one computer to another or other sources. It becomes active when you start an infected application or start your computer from a disk with infected system files. Once the viruses in the computer’s memory it usually infects any application to run. Different viruses behave in different ways. Some stay active in the memory until the computer is shut down or others may remain active only as long as the infected application is running.

Viruses are created by programmers who want to show off their programming skills. They are people who like to break the computer systems or networks. In this digital world, there are two different types of people who write computer virus programs Hackers and Crackers.


Hackers refer to the people who use their technical skills to enter into computer systems without admin permission. They are often computers enthusiast who break into either to gain knowledge about them or to pay a good prank. Many hackers are working with Government bodies and play a crucial role in solving cases.


On the other hand, Crackers are malicious programmers who gain unauthorized access to the computer system and destroy confidential or vital data present in the computers they invade. They often break the security of application software and create destructive programs like viruses.

What a Computer virus does?

The next question that pops in our minds is what a computer virus does. The virus tries to take control of the computer system, it has infected at the first opportunity available. Once entered, it starts making copies of itself and tries to carry out the harmful tasks written in its program. This process happens so quickly that the user is not even aware of the presence of a virus in his or her system or of the fact that anything unwanted is happening around.

Some viruses have a preset date and time at which they are programmed to activate themselves and halt the regular computing. Such viruses check the system Clock continuous, and when their time for date requirements are met, they can create havoc by performing harmful tasks listed in their program. A computer virus is incapable of performing specific tasks. It cannot infect files on right protected disk unlike CD ROM and cannot affect computer hardware, such as a mouse, monitor, and keyboard, and thus infects only software.

Viruses stay on the lookout for any new files or any new USB pen drives inserted into the system and attach the copies of themselves to these new files or USB pen drive. A computer virus is capable of performing these tasks and infects the system’s executable program files such as word processors, spreadsheets, and the operating system program.

It can also affect the disks by attaching itself to special programs in the hard drive called boot records (the programs the computer uses to start up it). Viruses are developed so it can infect the files before it is attached to an email message or transferred to a disk and thus spread from one computer another.

Computer Virus History

As long as any device has been stable enough to be useful, people have managed to find ways to cause problems. Humans intrigued nature and curiosity rose the invention of computer virus. However, the first virus was not built with the intent to harm but to create mischief on the computer.

The computer working virus works like their biological analog and a kind of software or program that infects a computer by self-replicating and spreading themselves to other machines. The program was designed to travel from one computer to another and can be copied to hundreds or thousands or possibly even millions of computers. Below given is the history of the development of viruses:

1. Creeper — 1971

In the early 70s, a program named Creeper was created by Bob Thomas of BBN and was released onto the ARPANET, where it would bounce around between computers. The only trace it left was a message printed out onto the teletype terminal reading, “I’m Nick Creeper catch me if you can.” The later versions of this program were amended and designed in such a way so it can leave a copy on the visiting machine. Thus, the creeper was the first virus program to automatically spread copies to different computers.

2. Reaper

Ray Tomlinson, tired of the nuisances’ program caused created the world’s second computer worm Reaper. It was initially designed to clean up the mess that the creeper had created across the network.

3. Animal and PERVADE — 1975

Animal was a text-based game developed by John Walker. It was a popular program among UNIVAC users where the computer would try to guess what the user was thinking of through a series of yes-or-no questions. With the help of the related program PERVADE, the copy of animal was made to every folder and directory the user had access to. As at that time, tape sharing was common practice, so ANIMAL was found on the systems where it had never been requested in the first place.

4. Elk Cloner — 1982

In 1982, a determined prankster Richard Scranton designed the world’s first computer virus. He wrote the Apple II program, as it was a soft target because at that that APPLE II stored its operating system on the floppy disk. The virus would copy itself around and spread by inserting itself into another personal computer. The virus replicates to the boot sector of the system disks used to boot the Apple 2, which in turn would then add the corner to every other disc loaded into the system.

5. Brain Virus — 1986

The brain virus is also known as the boot sector, or Pakistani brain was programmed by two Pakistani brothers. This virus’s original intent was to track how far it would spread to help with understanding the scope of software piracy. Still, later the two brothers were soon surprised to find out their programming vanished across the globe over to the United States. The brain virus quickly showed the potential widespread chaos and also did some real damage. It used to overwrite the large tables on disks and sometimes even going so far as to zero out the entire hard drive effectively destroying whatever data it contained and caused potential disasters for some businesses.

6. Morris Worm — 1988

In 1988, one of the largest viral viruses was the Morris worm, developed by Robert Morris in 1988. This worm had an inadequate mechanism to prevent a machine from being infected multiple times and was intended to allegedly highlight the security flaws of the academic networks. The worm bogged down 6000 machines to the point of uselessness. Indeed, the worm had done damage staking thousand to millions of dollars, giving Morris one of the first high profile convictions for the 1984 Computer Fraud And Abuse Act.

NOTE: The late 80s also introduced the first antivirus. A flu shot would embed itself within the operating system and alert the user anytime a program attempted to modify another file another. The common tactic was to search files or the boot sector for specific signatures associated with the virus.

7. Polymorphic- 1990

Mark Washburn introduced the polymorphic virus and was encrypted so that no two infections were alike. The standard tactic viruses used to spread across systems stealthily and remained dormant until a specific date or event.

8. Concept — 1995

With time and advancement, another development in the virus world was discovering the first macro virus in 1955 named ‘Concept.’ The macro virus was invented with an intend to infect the Microsoft Word documents. Though this virus was mostly harmless, it had open the doors for entirely new and much more dangerous vectors for infection after all sharing files were far more common sharing software, especially within businesses. Indeed, the trending technology ‘Internet’ had added advantage in the spread of the Malware.

9. Happy99–1999

The ‘Happy99’ had come in the picture of virus history on January 20, 1999. The worm would spread by email and invisibly attach themselves to whatever email Contacts the program would find. It displays a Happy New Year message and shows the fireworks to hide the changes that it had made. It tampers other system files, unlike Outlook and Internet Explorer.

10. I Love You — 2000

In 2000, the famous mischievous mass mailing malware Virus was the ‘I love you’ virus written in VBScript with engineering techniques. This worm spread by email and looked like a text file with a .txt file extension. It was offered as an attached love letter file from the previously infected victim and had given the file much thought, as it looked like a standard text file. So they would unintentionally activate the virus ‘I love you’ and its variants, and it spread across the globe in mere hours.

11. Blaster — 2003

Blaster exploits within Windows XP in 2000 and replicates themselves without any human intervention. This made them not only easy to catch but also extremely hard to isolate. Since they would continue to spread until the programmers manually removed blaster automatically.

12. Sasser — 2004

Sasser exploits a vulnerability in Microsoft windows. It generated traffic that brought many networks down and eventually ended up interrupting business and making modifications to other people’s systems without permission.

Types of Viruses

A computer virus is a kind of malicious program code that causes unexpected destructive impacts, unlike damaging the system software by corrupting or breaking the data. They possess the capability to be replicated from memory to memory over and over. The transmitting power is so quick from network to network that it can even hang the latest computer.

The types of viruses based on their origin, hiding, damaging, operating system, etc. It is not possible to name all the types of viruses because there are so many in the market, but the common and popular virus types are as follows:

1. Boot Sector Virus:

This type of virus infects the boot sector on the hard disk and other bootable records and media. This virus mostly spreads through portable media, unlike DVD or CD. The boot sector virus is likely known as one of the most dangerous viruses because they infect the master boot record. It is difficult to remove the boot sector virus as they usually end up with full system format. Thus, virus can become more overpowering if it has encrypted the boot sector and even can excessively damaged the code. The boot sector viruses include Michelangelo and stone.

2. Macro viruses:

As the name suggests, a macro is an original individual amongst the types of computer virus and is programmed to specifically targets macro language commands. They are designed in such a way that they can attach themselves to the legitimate word file present in a macro sequence. It contaminates the macros inside a pattern and gets involved it that pattern. Examples of macro viruses are Relax, Babbles, and Melissa.

3. File infector Virus:

This virus infect the program files such as applications (with .com or .exe extension files), games or utilities. If the infected program files are loaded into another system the virus is also loaded. File viruses can include program code or even can be sent as an email attachment. There are two types of file infected viruses:

· Direct action virus: This is also known as non-resident as it does not install itself or remain hidden in your computer’s memory. Most of the time it does not affect the system’s performance. It works by attaching itself to a file with .exe or .cm extension. When someone executes these application files, they get activated and starts looking for other similar application files within the directory so it could replicate. Example of this virus is Vienna.

· Resident viruses: These viruses install themselves on system and this virus performs its task even if the original infection files have been eliminated from the computer. These are more dangerous than direct action viruses depending on the programming of the virus. The user may find this virus tricky to identify and remove from the system. Example of resident viruses are CMG, Meve and Randex.

4. Companion viruses

Companion viruses are same as direct action types or resident types. They are named as companion because sometimes they involve into the matters and accompany of the other existing files. Examples of this viruses are Terax 1069 and Asimov 1539.

5. Multipartite virus

A multipartite virus may spread in multiple ways. It may take different actions on an infected computer depending on variables such as the operating system installed or the existence of individual files. They can simultaneously infect both sector and executable files. Thus, allowing them to act quickly and spread rapidly.

The two-sided adapt makes them tough to remove even if you clean a machine’s program files. It will immediately reproduce once you turn on the computer again if the virus remains in the boot sector. The example of these viruses includes tequila, flip, and invader.

6. Polymorphic Virus

Polymorphic viruses are one of the most difficult to detect for an antivirus program. Antivirus software can only blacklist one variant of a virus, but a polymorphic virus alters its signature or binary pattern every time it replicates. It looks like an entirely different piece of software to an antivirus program and therefore, can easily escape the blacklist and fool out the antivirus software. Thus, all the present cybercrimes depend upon this virus. The Polymorphic viruses include Marburg, Tuareg, Elkern, and Satan bug.

7. Spacefiller Virus

The Spacefiller virus is considered as one of the most intelligent viruses among its types. This virus works by attaching itself to the file without damaging the code or increasing its size. Often there are some empty within the data, and this virus tries to fit into that empty file space. Hence, they are also known as ‘cavity viruses. Thus, virus detection techniques usually bypass it. Luckily, this type of virus is comparatively rare as it was hard to code, and attackers are not acquainted with it much. But the increase of windows portable executable files are opening the doors for them.

8. Overwrite Viruses

The overwrite virus is one of the most annoying to the user though it is not particularly dangerous for your system. As the name suggests, this virus overwrites the original files with its code or sometimes deletes the content of the data which it infects. The only possible way to remove this virus is by deleting the file and losing it with the file contents, which could be crucial. It can affect both standalone files and standard software.

Override viruses are spread via email, and for a typical PC, it isn’t easy to identify. In the early 2000s, they were experiencing great success with windows 2000 and windows NT but are still prevalent and used in some sectors.

9. Rootkit Viruses

This virus is a type of malware that allegedly install an infected rootkit on your system without the admin’s knowledge. As a result, it gives the attacker the full authority to control the computer and alter the functioning of the computer’s programs and applications, copy the content, or even seize the confidential data. It can also trick the antivirus software. An example of the Rootkit virus is rootkit scanning.

How to Prevent Virus

You can never be too careful when it comes to computer security. Your system is open to many security breaches from phishing sites (to steal your passwords), ransomware that encrypts your data, secret trojan horses, worms, or malicious malware. But most of these risks and viruses can be subdued if you do some regular clean-ups and avoid fake software and websites.

1. Keep your system and software up to date: Many programmers use Java, and it is installed practically on every coder’s system. Thus, it is a huge target and more prone to security risks. Different software launches the update program to maintain the security and confidentiality of data. Upgrade your operating system to Windows 10 as it has inbuilt software to protect the windows directly. Apart from this, make sure that routers firmware, antivirus, or other software’s are up to date.

2. Try to use strong passwords: We all want everything accessible and relatable around us. When it comes to passwords, we use our name, phone numbers, date of birth, or the commonly used one abc@123. But, all these fall under the common password category and opens the door for security breaches. The hacker can gain access to your data and possibly could tamper or reset it. The best way to set a password is by using lower case, upper case, digit, and special characters.

3. Use Antivirus Software: As Antidote is the vaccine for the biological virus, similarly, antivirus software works like a vaccine to fight against computer virus. It eliminates or blocks the virus even before you get aware of it. Scan your system regularly and clean up the junk files and folders.

4. Use a Firewall: The firewall ensures that your system is encrypted with an extra layer of protection. Mac’s or many modern Pc’s have inbuilt firewall software installed. Make sure that it is always enabled.

5. Aware of Email Scams: Most of the macro viruses enter your system through Email. Do not accept emails or open attachment from an unknown maid id even if you have downloaded the file scanning before running is always advisable. However, your antivirus software will automatically do that in the backend.

6. Avoid using open Wi-Fi: Whenever we are Café, Club, Coffee shop, or airports, the open WI-Fi is always a significant pact. But have you ever wondered how hazardous it could be if we connect to those public resources? A hacker can install a trained virus code in our system by using them, and rest is known.

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