In the realm of cybersecurity, a virus is a type of malicious software (malware) that, when executed, replicates itself by modifying other computer programs and inserting its own code. The term “virus” is often used as a generic reference to any malicious code that is not, in fact, a true computer virus. This document discusses the concept of a computer virus in detail, its types, how it spreads, its impact, prevention methods, and how to deal with a virus infection.

Understanding the nature of computer viruses is crucial in today’s digital age. With the increasing reliance on technology and the internet, the risk of encountering such threats has also risen. This glossary entry aims to provide an in-depth understanding of what a computer virus is, how it works, and how it can be prevented and removed.

Definition of a Virus

A computer virus is a type of malicious software program (“malware”) that, when executed, replicates itself by modifying other computer programs and inserting its own code. It is a hidden piece of code embedded within a legitimate program. This code is designed to execute when its host program is run, allowing the virus to infect other programs and systems.

Viruses can have various impacts, from annoying effects such as slowing down the system to destructive outcomes like deleting files or causing system crashes. The term “virus” comes from the way these software spread, which is similar to biological viruses.

Origin of the Term

The term “virus” in the context of computers was first used in a 1984 paper by Fred Cohen, who described it as “a program that can ‘infect’ other programs by modifying them to include a possibly evolved copy of itself.” The analogy with biological viruses was drawn because of the replication and spreading mechanism that computer viruses employ, similar to biological viruses.

The first computer virus, known as “The Creeper”, was detected on ARPANET, the forerunner of the internet, in the early 1970s. It was an experimental self-replicating program written by Bob Thomas at BBN Technologies. However, it was not malicious like modern computer viruses, but it paved the way for the viruses that would follow.

Types of Computer Viruses

There are several types of computer viruses, each with unique characteristics and methods of operation. Some of the most common types include boot sector viruses, direct action viruses, resident viruses, multipartite viruses, polymorphic viruses, and macro viruses.

Each type of virus has a unique method of infecting and damaging the systems or files that it targets. Understanding these types can help in identifying and removing the virus and also in taking preventive measures.

Boot Sector Viruses

Boot sector viruses are a type of virus that infects the boot sector of a hard drive or removable storage media like a flash drive. This type of virus is particularly dangerous because it loads onto the computer’s memory each time the system is booted up. From there, it can infect any file that the system accesses.

Examples of boot sector viruses include the infamous ‘Stoned’ virus, ‘Michelangelo’, and ‘Elk Cloner’. These viruses were prevalent in the era of floppy disks, but the advent of modern operating systems which do not allow direct disk sector access has made them less common today.

Direct Action Viruses

Direct action viruses are a type of virus that attaches itself to executable files and replicates when the infected file is executed. These viruses are not memory-resident; instead, they act and then remove themselves, only to act again when the file they are attached to is executed again.

Direct action viruses primarily aim at spreading infection and can be easily detected and removed with an antivirus program. An example of a direct action virus is the ‘Vienna virus’.

How Viruses Spread

Computer viruses spread in a number of ways. The most common method is through email attachments or instant messaging. They can also spread through infected websites, downloaded files, social media links, network connections, and even through physical media like USB drives.

Once a virus has infected a system, it can spread to other systems through network connections or by infecting files on a network drive. It can also spread by infecting files on a USB drive, which is then used on another system.

Through Email and Instant Messaging

Email and instant messaging are one of the most common methods of virus transmission. Viruses are often attached to an email or instant message as a hidden piece of code. When the recipient opens the attachment or clicks on a link, the virus is activated.

These types of viruses often trick the recipient into opening them by pretending to be something else. For example, a virus might be disguised as a document or image file, a link to a website, or even a video or music file.

Through Infected Websites and Downloaded Files

Another common method of virus transmission is through infected websites and downloaded files. Some websites are specifically designed to infect visitors, while others may be legitimate websites that have been compromised by hackers.

Downloading files from the internet can also lead to a virus infection. This is especially true for files downloaded from untrustworthy sources. Some viruses can even disguise themselves as legitimate software, tricking the user into downloading and installing them.

Impact of Viruses

The impact of a computer virus can range from minor annoyances to serious disruptions. Some viruses are relatively harmless and may simply cause your computer to run slower or display annoying pop-ups. However, others can cause serious damage, such as deleting files, stealing personal information, or even rendering your computer unusable.

Regardless of the severity of the virus, it’s important to take any potential infection seriously. Even a minor virus can become a major problem if it’s not dealt with promptly and properly.

Data Loss

One of the most serious impacts of a computer virus is data loss. Some viruses are designed to delete files or entire sections of a hard drive. This can result in the loss of important documents, photos, and other data. In some cases, this data may be recoverable, but in others, it may be permanently lost.

Data loss can have serious consequences, especially for businesses. It can result in lost work, disrupted operations, and even legal issues if the lost data includes sensitive customer information.

Identity Theft

Some viruses are designed to steal personal information. This can include passwords, credit card numbers, and other sensitive data. The virus may then transmit this information back to the hacker, who can use it for identity theft or other fraudulent activities.

Identity theft can have serious consequences, including financial loss, damage to your credit rating, and even legal problems. It can also be difficult and time-consuming to resolve.

Preventing Virus Infections

Preventing virus infections is a critical aspect of maintaining a secure computer system. There are several strategies that can help prevent virus infections, including the use of antivirus software, keeping your system and software up to date, avoiding suspicious emails and websites, and practicing safe internet habits.

While no strategy can guarantee 100% protection against viruses, these methods can significantly reduce your risk of infection.

Use of Antivirus Software

Antivirus software is a critical tool in preventing virus infections. This software is designed to detect and remove viruses before they can cause damage. It works by scanning your computer for known viruses and monitoring your system for suspicious activity.

It’s important to keep your antivirus software up to date, as new viruses are constantly being created. Most antivirus software can be set to update automatically.

Keeping System and Software Up to Date

Keeping your system and software up to date is another important strategy for preventing virus infections. Many viruses exploit vulnerabilities in outdated software, so keeping your software up to date can help protect against these threats.

Most operating systems and software have automatic update features. It’s a good idea to enable these features to ensure that your system and software are always up to date.

Dealing with Virus Infections

If your computer is infected with a virus, it’s important to deal with it as quickly as possible to minimize the damage. The first step is to isolate the infected system to prevent the virus from spreading. Then, use your antivirus software to scan your system and remove the virus.

If your antivirus software is unable to remove the virus, you may need to seek professional help. In some cases, it may be necessary to wipe your system and reinstall your operating system and software.

Isolating the Infected System

If your computer is infected with a virus, the first step is to isolate the system. This means disconnecting it from any networks it’s connected to and avoiding using any removable media such as USB drives. This is to prevent the virus from spreading to other systems.

It’s also a good idea to backup any important data if possible. However, be careful not to backup any infected files. This could lead to the virus being reintroduced when you restore your data.

Using Antivirus Software

Once you’ve isolated the infected system, the next step is to use your antivirus software to scan your system and remove the virus. Most antivirus software has a scan feature that you can use to check your system for viruses.

If the antivirus software detects a virus, it will typically try to quarantine or delete the infected files. In some cases, the antivirus software may be able to repair the infected files.

Seeking Professional Help

If your antivirus software is unable to remove the virus, or if the virus has caused significant damage, you may need to seek professional help. This could involve taking your computer to a professional repair service or hiring a cybersecurity expert.

Professional help can be expensive, but it may be necessary if the virus has caused serious damage or if your data is at risk. It’s also important to consider the potential cost of not seeking professional help, such as the loss of important data or the risk of identity theft.


Computer viruses are a serious threat in today’s digital world. They can cause a range of problems, from minor annoyances to serious disruptions. Understanding what a computer virus is, how it works, and how to prevent and remove them is crucial for maintaining a secure system.

While it’s impossible to completely eliminate the risk of virus infections, by following the strategies outlined in this glossary entry, you can significantly reduce your risk and ensure that you’re prepared to deal with any potential virus infections.

With cybersecurity threats on the rise, organizations need to protect all areas of their business. This includes defending their websites and web applications from bots, spam, and abuse. In particular, web interactions such as logins, registrations, and online forms are increasingly under attack.

To secure web interactions in a user-friendly, fully accessible and privacy compliant way, Friendly Captcha offers a secure and invisible alternative to traditional captchas. It is used successfully by large corporations, governments and startups worldwide.

Want to protect your website? Learn more about Friendly Captcha »