What is a Computer Virus? Everything You Need to Know (2023)

By Tibor Moes / Updated: June 2023

What is a Computer Virus? Everything You Need to Know (2023)

What is a Computer Virus?

In today’s digital world, computer viruses have become an unfortunate reality that many of us have experienced firsthand. They can cause serious damage to our devices, compromise our personal information, and even lead to significant financial loss.

But what is a computer virus exactly, and how can we prevent its devastating effects? This comprehensive guide will delve into the world of computer viruses, providing you with insights into their transmission methods, types, and prevention strategies.


  • A computer virus is a type of malicious software that, when executed, replicates itself by modifying other computer programs and inserting its own code.

  • Viruses can cause various damages such as data corruption, system performance degradation, or unauthorized access to private information.

  • Preventing viruses involves regular system updates, using reliable antivirus software, and safe browsing habits.

Don’t become a victim of cybercrime. Protect your devices with the best antivirus software and your privacy with the best VPN service.

Defining a Computer Virus

A computer virus is a type of malicious software designed to infect and cause harm to computer systems. Just like a biological virus, a computer virus attaches itself to a host program, file, or document and remains dormant until the computer executes it. Once activated, a computer virus can cause a wide range of damage, from deleting files to stealing sensitive information.

Computer viruses spread by attaching themselves to executable files or programs, then replicating when the host file is opened. They can spread through networks, external drives, file-sharing programs, and infected email attachments. The primary purpose of a computer virus is to infect and damage computer systems, making them a significant threat to personal and professional computing environments.

The Lifecycle of a Computer Virus

Understanding the lifecycle of a computer virus is crucial for effectively preventing and addressing infections. A computer virus typically goes through four phases in its lifecycle: dormant, propagation, triggering, and execution.

In the following subsections, we will delve deeper into each of these phases, providing a clearer picture of how viruses function and spread.

Dormant Phase

During the dormant phase, the virus lies inactive within the host computer, waiting for specific conditions to be met or actions to be taken by the user. This phase allows the virus to avoid detection and remain hidden until the conditions are right for it to become active and start causing damage. Not all viruses have this phase, but those that do can be particularly challenging to detect and remove.

Once the required conditions are met or the user takes the necessary action, such as opening a file or clicking a link, the virus becomes active and moves onto the next phase of its lifecycle. This transition leads to the propagation phase, where the virus begins to spread and infect other programs or areas within the computer system.

Propagation Phase

The propagation phase is when the virus starts to reproduce and spread throughout the computer system. During this phase, the virus creates copies of itself and inserts these replicas into other programs or specific areas of the system disk, allowing it to spread to other computers. The ability to propagate is a key characteristic of computer viruses, making them particularly difficult to contain and eliminate.

As the virus spreads and infects more files and programs, it increases the likelihood of being discovered and activated by the user. Once the virus has successfully propagated, it moves on to the triggering phase, during which it becomes activated and starts to execute its malicious payload.

Triggering Phase

The triggering phase is a crucial part of a computer virus’s lifecycle, as it is the moment when the dormant virus becomes active and begins to cause harm. Various system events or user actions can set off the triggering phase, such as opening an infected file, clicking a malicious link, or encountering specific conditions within the computer system.

Once triggered, the virus initiates its harmful activities, potentially leading to data loss, system crashes, or unauthorized access to sensitive information. The virus’s true capabilities are revealed during the execution phase, as it carries out its intended purpose and wreaks havoc on the infected system.

Execution Phase

The execution phase marks the culmination of the computer virus’s lifecycle, as it unleashes its payload and carries out its destructive activities. Depending on the specific virus, these activities can include stealing data, destroying files, or disrupting services on the network or local device. The execution phase is when the virus’s impact is felt most significantly, causing users to scramble for solutions to remove the infection and mitigate the damage.

Some viruses, like direct action viruses, can cause particularly severe damage to the infected system by attaching themselves to COM or EXE files and then deleting themselves, leaving a trail of destruction in their wake.

Understanding the execution phase and the potential damage it can cause is essential for effectively addressing and removing a computer virus infection.

Common Symptoms of a Computer Virus Infection

Recognizing the common symptoms of a computer virus infection is vital for early detection and prompt removal. Some of the most common signs that a computer may be infected with a virus include slow performance, pop-up ads, and unexpected program behavior. Other indicators of a potential virus infection may include frequent crashes, system slowdowns, and unexplained file or data loss.

In some cases, computer viruses can even compromise personal information, such as usernames, passwords, and credit card details, leading to identity theft and financial loss. As such, it is crucial to remain vigilant and take action at the first sign of a potential virus infection to minimize the damage and protect your sensitive information.

Methods of Computer Virus Transmission

Computer viruses can be transmitted in various ways, making it essential to understand their methods of transmission to effectively protect your system. Some common ways in which computer viruses spread include email attachments, downloads, infected hardware, and social media links. By exploiting these channels, viruses can quickly spread from one device to another, posing a significant threat to users and systems alike.

To reduce the risk of infection, it is crucial to be cautious when opening email attachments, downloading files, or clicking links from unfamiliar sources. Additionally, ensuring that your computer’s hardware and software are regularly updated and protected by reliable antivirus software can help minimize the risk of transmission and keep your system safe from viruses and other malware.

Types of Computer Viruses

There are several different types of computer viruses, each with their unique characteristics and methods of infection. In the following subsections, we will explore some of the most common types of computer viruses, including boot sector viruses, resident and non-resident viruses, and polymorphic viruses, to better understand their behavior and potential impacts on computer systems.

Boot sector viruses are malicious programs that infect the boot sector of a computer’s hard drive. They are usually spread through floppy disks or other removable media. Resident viruses are programs that remain.

Boot Sector Virus

A boot sector virus infects the boot sector of a computer’s hard drive, which is responsible for loading the operating system during the startup process. These viruses can spread through hardware such as floppy disks, USB drives, and CDs, and are activated when the infected device is connected to the computer during startup.

The presence of a boot sector virus can lead to various issues, such as boot-up problems, sluggish system performance, and difficulties locating the hard disk. To protect your computer from boot sector viruses, it is essential to ensure your disks are write-protected and avoid starting your computer with untrusted external drives connected.

Resident and Non-Resident Viruses

Resident viruses differ from non-resident viruses in their method of infection and spreading. A resident virus remains in the computer’s memory even after the host program or application has stopped running, allowing it to continue causing damage and infecting other files.

In contrast, a non-resident virus does not reside in the computer’s memory and is not executed from there. The key distinction between resident and non-resident viruses is their presence in the computer’s memory, with resident viruses being more difficult to detect and remove due to their ability to persist even after the host program has been closed.

Polymorphic Virus

Polymorphic viruses are a particularly dangerous type of computer virus, as they have the unique ability to change their code in order to evade detection by antivirus software. They use encryption keys and a mutation engine to constantly alter their shape and signature, making it difficult for antivirus programs to identify and remove them.

To protect against polymorphic viruses, it is essential to use reliable antivirus software, keep all software up-to-date, and exercise caution when handling suspicious emails and websites.

Prevention Strategies for Computer Viruses

Protecting your devices from computer viruses requires a combination of best practices and tools. Some key prevention strategies include using antivirus software, regularly updating programs and operating systems, and avoiding suspicious links or downloads. By implementing these measures, you can reduce the risk of infection and keep your devices safe from viruses and other forms of malware.

In addition to these basic precautions, it is also important to maintain a healthy sense of skepticism when encountering unexpected offers, links, or attachments in emails and messages. Using a secure browser, avoiding pirated software, and downloading apps or programs only from trusted sources can further help protect your devices from potential virus infections.

Removing a Computer Virus

If you suspect your computer is infected with a virus, it is essential to take swift action to identify and remove the infection. There are two primary methods for removing a computer virus: manually identifying and deleting the virus or using antivirus software to detect and eliminate the infection.

Manual removal can be challenging and time-consuming, as it requires a thorough understanding of the virus’s behavior and characteristics. On the other hand, using antivirus software provides a more efficient and reliable way to remove the infection and safeguard your system from future threats.

Regardless of the method chosen, it is crucial to act quickly to minimize the damage and protect your sensitive information.

Real-Life Examples of Computer Viruses

Throughout history, there have been numerous examples of computer viruses causing significant damage and disruption to computer systems and users. Some of the most notorious computer viruses include Melissa, ILOVEYOU, Code Red, Klez, Sobig, Mydoom, Sasser, and Zeus. These viruses have caused widespread data loss, system crashes, and unauthorized access to sensitive information, highlighting the importance of understanding and addressing computer virus infections.

By studying these real-life examples, we can gain valuable insights into the behavior and impact of computer viruses, allowing us to develop more effective prevention strategies and response plans. This knowledge can help protect our devices and personal information from the devastating effects of future virus infections.

Differentiating Between Viruses and Other Malware

While computer viruses are a significant threat, it is important to recognize that they are just one type of malware. Other forms of malware, such as worms, Trojans, and ransomware, also pose risks to computer systems and users. Understanding the distinctions between viruses and other types of malware can help you better protect your devices and take appropriate action when faced with a potential infection.

One key difference between a computer virus and a worm, for example, is that a worm can spread between systems and networks without requiring any user action or a host system, while a virus relies on user interaction to execute its code and propagate. By familiarizing yourself with the various types of malware and their characteristics, you can enhance your cybersecurity measures and safeguard your valuable data.


In conclusion, computer viruses are a prevalent and dangerous threat to computer systems and users worldwide. By understanding their nature, lifecycle, transmission methods, and various types, we can better protect our devices and personal information from potential infections. Implementing prevention strategies, such as using antivirus software, updating programs regularly, and exercising caution when handling suspicious links or downloads, is crucial for maintaining a secure computing environment.

As technology continues to evolve and new forms of malware emerge, it is essential to stay informed and vigilant in safeguarding our digital lives. By taking proactive steps to protect our devices, we can minimize the risk of computer virus infections and ensure that our valuable data remains safe and secure.

How to stay safe online:

  • Practice Strong Password Hygiene: Use a unique and complex password for each account. A password manager can help generate and store them. In addition, enable two-factor authentication (2FA) whenever available.
  • Invest in Your Safety: Buying the best antivirus for Windows 11 is key for your online security. A high-quality antivirus like Norton, McAfee, or Bitdefender will safeguard your PC from various online threats, including malware, ransomware, and spyware.
  • Be Wary of Phishing Attempts: Be cautious when receiving suspicious communications that ask for personal information. Legitimate businesses will never ask for sensitive details via email or text. Before clicking on any links, ensure the sender's authenticity.
  • Stay Informed. We cover a wide range of cybersecurity topics on our blog. And there are several credible sources offering threat reports and recommendations, such as NIST, CISA, FBI, ENISA, Symantec, Verizon, Cisco, Crowdstrike, and many more.

Happy surfing!

Frequently Asked Questions

Below are the most frequently asked questions.

What can cause a computer virus?

It’s important to be aware that computer viruses can be caused by downloading malicious content, clicking on suspicious links or email attachments, connecting an infected device like a USB stick, or simply visiting untrustworthy websites.

To avoid this, you should practice safe browsing habits and always keep your antivirus software updated.

What is a computer virus and how is it harmful?

A computer virus is a malicious program that can cause harm to your computer, including data loss or system malfunctions. It spreads through downloading software or files from the internet, opening an infected email, or plugging in an infected external device.

This can be very damaging as it can lead to system errors, data corruption, and crashes.

Author: Tibor Moes

Author: Tibor Moes

Founder & Chief Editor at SoftwareLab

Tibor is a Dutch engineer and entrepreneur. He has tested security software since 2014.

Over the years, he has tested most of the best antivirus software for Windows, Mac, Android, and iOS, as well as many VPN providers.

He uses Norton to protect his devices, CyberGhost for his privacy, and Dashlane for his passwords.

This website is hosted on a Digital Ocean server via Cloudways and is built with DIVI on WordPress.

You can find him on LinkedIn or contact him here.

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