What Is a Computer Virus?

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There are many ways you can tell a virus has infected your computer. You may notice reduced performance, missing or duplicated files, performed actions you don’t remember taking, a sudden crash of your hard drive, or glitches when using your computer. 

This post will look into viruses and other malware types and how they spread. Finally, we share tips on protecting your computer from getting infected. So, before we delve into all the technicalities, the first question to address is: What is a computer virus?

Computer Virus Definition

A computer virus is a malicious program written by hackers. Viruses have many purposes, some are created to simply cause a nuisance, but they may try to collect or destroy sensitive data. Viruses present a severe cybersecurity threat. The information collected could even be used to commit serious crimes like identity theft. 

It is not enough to answer the question “What is a computer virus?” with only a definition. We also need to shed some light on how these viruses operate for more context. Do not confuse computer viruses with other malware types that can attack your device, such as spyware or ransomware, as they have different goals and MO. 

Like biological infections, computer viruses need a host program to leech onto and are prone to spreading. Once it is downloaded to a computer, a virus will likely require you to do something to activate transmission.

After this, the virus will self-replicate to infect as many devices as possible. Bits of malicious code usually get attached to other files on the computer and spread, creating a vile circle that could lead to drastic results if not expediently dealt with.

Malignant computer programs share more than their name with living viruses. Viruses in a flu attack can be spread with simple actions like handshakes with an infected person. The viruses attach to a healthy human cell (which will be “healthy” programs and software for our purpose), then reproduce more viral cells.

In a computer virus attack, the action taken to occasion a spread could be downloading files from unsecured sources on the internet, opening suspicious email attachments, or directly transferring infected files from one computer to the other. 

Not all viruses will act in this way. Instead of the flu-like course of waiting for an action or command that triggers them and their replication, they could begin operating as soon as they get on a new computer.  

Computer Virus Signs

Computer viruses might not be immediately recognized as a virus. This is because they attack the computer’s programming functions, which are not always visible. There are function-specific symptoms that can help detect the presence of viruses on computers. Below are some of the signs of a computer virus you may notice:

1. Pop-up windows

Internet surfing may become tedious or annoying on a virus-infected computer due to frequent unsolicited pop-up windows. In some cases, windows will pop up on each click, while in other cases, they pop up without clicks and at will. These pop-ups do not only indicate the presence of a virus but could also lead to more infections on the computer.

2. Self-operation

When your computer begins to act like it has a mind of its own, it hints at a computer virus attack. You will notice that files and applications launch by themselves and stay running in the background, which causes a slower function rate and rapid battery drainage. A virus can also manifest through file deletion or the appearance of new apps. 

3. Computer slows down 

A computer virus can generally affect the rapidity of computer functions, not only when files and applications are running in the background. It can become increasingly difficult to launch files and for the computer to perform basic functions. 

4. Security breaches

Of all the signs of a computer virus, a security breach is the most undesirable. This kind of virus attack focuses on personal data on your device. The most common occurrence is that users get logged out of password-protected accounts and websites because their password encryption has been compromised. 

5. Device crash

Device crash is probably the most extreme sign of virus infection. The chances of a repair, in this case, are very slim. The virus has had to infect many files and applications for the situation to get this dire. When dealing with a device crash, it’s best to look for professional help.

Types of Computer Viruses 

Understanding what a computer virus is, is only the beginning of your quest for a virus-free life. Different viruses affect different files or components on your device, which means that determining the location and extent of the damage can point you toward the solution. 

Another important distinction is the kind of virus you are dealing with. Let’s look at some common types:

Boot Sector Virus

As the name implies, a boot sector virus infects a hard disk’s master boot record function. The virus gets activated through the hard disk at booting or starting up the computer. Boot sector virus is commonly transferred to a computer through pluggable devices such as USB drives and CD-ROMs.

Direct-Action or Nonresident Virus

Direct action viruses are the most common of the fold and the easiest to create. They are designed to copy their code to executable programs from where they self-replicate. Nonresident viruses are often found in programs requiring permission to run but can infect files even when the programs are not running.

Resident Virus 

As the name implies, resident viruses are likely to stick around long after doing the damage they were created to do. Unlike the direct-action variant, resident types of computer viruses pitch their tent in a computer’s primary memory, the RAM

Multipartite Virus

These viruses influence several parts of the computer and various kinds of files. It’s safe to refer to them as a combination of other viruses, for example, the boot and nonresident viruses. Multipartite viruses simultaneously attack affected files and the computer’s boot sector

Polymorphic Virus

Polymorphic viruses are tricky because they are not easy to detect. They can morph into harmless programs to avoid being noticed. These types of computer viruses will keep their harmful capabilities after morphing and, even when caught, can be a hassle to get rid of. Detection is usually partial, making complete removal a mean feat to achieve.

Macro Virus

The macro viruses are usually written in the macro programming language, thus the name. Macro viruses can be easily embedded within the software written in the same language. Think again if you ever believed that Microsoft Word couldn’t be prone to virus infections. Microsoft Word, PowerPoint, and Excel are among the most targeted programs for these computer viruses.

Overwriting Virus

Overwriting viruses are slow and steady. They overwrite or delete existing programs with malicious codes. Overwriting viruses are considered the most harmful because of their elegant operation and their ability to cause severe damage to a computer’s performance. They usually spread via emails.

File Infector Virus

These viruses will start by infecting a single file and eventually spread to other files and programs. Once an affected file is loaded, the virus follows suit. File infector viruses are often passed around through games and word processors. They can affect files in formats such as .com, .exe, .sys, .ovt, .prg, .mnu, and so on.

Spacefiller Virus

Spacefiller viruses, also known as cavity viruses, complete the empty spaces in a code without changing the file’s size. Their detection can be a challenge even for good antivirus software. The good news is that spacefiller viruses are rare.

Computer Viruses vs. Other Malware

The two terms – computer viruses and malware are often used interchangeably but are, in fact, two different things. To distinguish between them, one can say that every computer virus is malware, but not every malware is a computer virus

Unlike a virus that needs action like launching a file to put it in motion, most malware only needs to infect the computer to function. It means it can work actively or spread without any action. A classic example of malware that can operate independently is a computer worm.

Some types of malware are more dangerous to computers than simple viruses. They are often used for large-scale hacking activities that viruses can’t be used for. Some examples include:


Ransomware is malware that uses encryption to hold users’ data for ransom. In simpler terms, malicious actors use it to steal data or encrypt it, leaving the user without access. Hackers then offer you a decryption key to regain access to the hijacked systems in exchange for money. However, even if you meet their demands, there’s no guarantee they’ll honor their side of the deal.


A computer worm targets networks. If worms infect one computer in an organization, it is very likely to infect all its computers. Worms replicate themselves efficiently and may pose a serious threat.


The name of this malware comes from an episode in ancient Greek history when Spartans, who besieged the city of Troy, used a wooden horse to hide soldiers in it and smuggle them into the city. 

This illustrates the way a malicious Trojan program functions. It may seem like legitimate software or a file to trick you into installing it on your device. Trojans may even pose as the remedy for a virus infection but turn out to be viruses once installed.

Just as there are similarities between various types of computer viruses, there are also cases where different malware types work together. For example, some ransomware can behave like a Trojan to access the computer. 


Like Trojans, adware seems harmless on face level. It’s similar to one of the computer virus examples listed above – the spacefiller virus. 

Adware can have malicious tendencies because it pools your data without consent and feeds you ads based on the collected information. This is dangerous as pop-up ads often conceal computer viruses that can infect the computer with one click. The good news is that adware is relatively easy to detect and remove from most devices.


Hackers mainly use this malware to monitor a target’s computer activities and gather sensitive data such as passwords and keystrokes. Like adware, spyware is usually easy to detect and get rid of.

Computer Virus Protection 

As you can see, computer viruses can cause all sorts of damage. The good news is that, with some simple precautions, you can protect yourself against most computer viruses. In this section, we’ll give you a few tips on how to keep your computer malware-free.

Situational Awareness

Situational awareness in cybersecurity describes alertness while surfing the internet or using a computer. Ensure that you are on the lookout for threats that may pop up in those activities. This is the first step towards guarding yourself and your devices from eventualities.

Also, beware when using emails. The effect of a virus infection via email can be drastic, especially when the email is connected to the network of the organization you work for.

Computer viruses are often embedded in email attachments and links. Watch out for the misspelled words in the email address. The average person reads a mail without verification of the email address and goes ahead to click links because they have assumed the sender is legitimate. 

Another thing to note in emails is grammar and flow of sentences. If these do not make sense, the email is likely a scam.

Invest in Reliable Cybersecurity Software

Another way to guard against any computer virus is to use antivirus or anti-malware software that you can trust. It is best to choose a reliable antivirus that can detect the presence of a computer virus immediately. 

The antivirus software will conduct periodic scans to let you know if there are existing vulnerabilities. Automatically removing a computer virus when detected is another sign of a good antivirus. You do not have to lift a finger afterward because the antivirus does the job on your behalf.

Also, ensure that the antivirus you have selected is compatible with your device and its operating system. This is important because the top antivirus solution for Mac devices, for example, will not always be the best for devices operating on Windows.

Final Thoughts

Having answered the most important question, “What is a computer virus?” we have understood the basics of viruses and the importance of being cautious when handling emails from unknown senders, visiting suspicious websites, or downloading files from unverified sources. Phishing sites are also known for constant pop-up ads that you inadvertently click on due to their indiscriminate and unorganized ways.

You can never be too careful, and an excellent place to start is to purchase reliable antivirus software to keep the hackers at bay. 

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