What is a Computer Virus?

In today’s digital age, the term “computer virus” is almost as well-known as the common cold, yet the term is frequently misunderstood. At their most basic, a computer virus is a type of malicious software that self-replicates. They may disrupt the normal functionality of a computer system, steal your personal data, or even use your computer to mine cryptocurrency.

Understanding how computer viruses work, spread, and manifest can help you keep your computer, and your digital life, safe and secure.

Depiction of a trojan virus with a red Knight horse from a chess board over binary code

How do computer viruses work?

A computer virus is designed to attach itself to a host program and run when that program is executed. Like biological viruses, computer viruses rely on hosts to spread and replicate. This is distinct from a computer worm – which is entirely self contained and needs no user-action to release its nefarious payload.

Once activated, a computer virus may perform a variety of disruptive tasks ranging from corrupting data to commandeering system resources.

How do computer viruses spread?

Viruses spread in various ways, including via email attachments, malicious website downloads, and infected USB drives. They can also propagate through network vulnerabilities or may exploit security flaws in software.

Seemingly legitimate software may be bundled with a virus – tricking users into downloading them.

Common Signs of Computer Viruses

Some computer viruses are stealthy, quietly lurking in the background while passing along your keystrokes, including usernames and passwords, in real-time. For these threats, a firewall may be your best defense, but the unfortunate reality is that your first sign of trouble might come in the form of identity theft.

However, many viruses are less subtle and will leave tell-tale signs that a savvy user can notice.

Pro-tip: Using multi-factor authentication (MFA) is one of the best ways to protect yourself online. This way even if your passwords are compromised your accounts will still have another layer of protection.

System speed

A significant slowdown in your computer’s performance can be a red flag. This happens when the virus consumes valuable system resources. Some types of viruses use your computer to mine for cryptocurrency – a process that is highly system intensive and will result in a noticeable degradation of performance.

On Windows computers you can monitor your computer resource usage via the task manager. The task manager can be opened by pressing Control+Shift+Escape (or Control+Alt+Delete on older versions of Windows).

Alternatively, your computer fan can act as a rough guide to CPU usage. If your fan is running at full speed even when you’re not doing anything, something may be amiss.

Frequent pop-up windows

Unexpected or frequent pop-up windows appearing on your screen is a sign that your computer is infected with a type of virus known as adware. Sometimes viruses will even present you with messages claiming that your computer is infected with a virus and direct you to purchase a fake anti-virus!

While legitimate security software may prompt you to buy a professional version, a virus protection tool that forces you to pay to remove a virus is a scam! Do not believe the message and seek the help of a professional virus and malware removal specialist.

Self-executing programs

If programs or applications open and close automatically without your intervention, this may indicate virus activity. Some legitimate programs will cause this behavior as well – so this is not a guarantee that your computer is infected.

Accounts being logged out

Unexpected logouts from your user accounts, especially email and social media, can be a symptom of some types of malware. In some cases this is completely innocuous, for example if your browser is set to clear cookies when you close it, but if the behavior is new and unexplained you should be on your guard.

Frequent crashes

If your computer crashes or freezes often, this might be due to malicious code affecting your system stability.

In Windows computers this may take the form of the Blue Screen of Death, where you are presented an error message atop of a solid blue background. If you are using an Apple product the crash screen is known as a kernel panic and is a black screen with an error message atop it.

Mass emails being sent from your account

If friends or colleagues report receiving strange emails from you that you did not send, a virus may be the culprit. Many types of malicious programs spread by sending infected emails to your entire contact list. For this reason it is important to be wary of all email attachments – even if they come from a known sender!

Homepage changes

If the homepage of your web browser changes itself, this is a sign that your computer is infected with a virus. In some cases viruses may change your homepage to a spammy search engine – any searches you conduct using this webpage will generate income for the cybercriminal behind it.

Types of Computer Viruses

Resident Virus

A Resident Virus resides in a computer’s memory (RAM, not hard drive) and operates without user intervention. It becomes active each time the operating system runs and can silently cause damage in the background.

Multipartite Virus

A Multipartite Virus combines the characteristics of multiple types of viruses, making it particularly difficult to remove. It can spread in various ways and perform a range of malicious actions.

Direct Action Virus

The Direct Action Virus attaches itself to an executable (.exe) file and activates when the infected file is opened.

These viruses only take action when the file is opened – which is a great reason you should always scan downloaded files before opening them!

Browser Hijacker

A Browser Hijacker redirects your web browser to unwanted websites without your permission. This type of virus often aims to generate advertising revenue.

Overwrite Virus

An Overwrite Virus deletes data in the files it infects, rendering them useless and leading to a loss of data or functionality. This is often a component of ransomware where victims are prompted to pay a ransom or else the virus will wipe out their data.

Note: The vast majority of people who pay the ransom for a ransomware attack do not recover their data. Your best bet is to contact a cybersecurity company and seek professional help.

Virus depicted on microchip

Web Scripting Virus

The Web Scripting Virus exploits the code of web browsers to carry out its malicious actions. It often infects a user’s computer when they visit a compromised website from an out of date browser.

File Infector Virus

File Infector Viruses focus on infecting executable files. When these infected files are executed, the virus activates and may infect other files or carry out other malicious activities.

Network Virus

A Network Virus is designed to spread across computer networks by exploiting vulnerabilities. This type of virus can be particularly problematic for businesses and other large organizations, but with the increasing number of connected devices even household networks are at risk.

Internet of Things (IoT) devices, like internet connected appliances, thermostats, and security cameras, can be at particular risk as these devices are infrequently updated.

Boot Sector Virus

A Boot Sector Virus infects the Master Boot Record (MBR) of a computer. Boot sector viruses of the past commonly infected floppy disks and hard drives and have become far less common as computers moved away from DOS commands. However, rootkits are essentially the modern version of a boot sector virus and present similar threats to their antecedents.

These viruses infect your computer at the level of BIOS – the code which allows your operating system to run – and thus are very difficult to remove. Even formatting your harddrive does not remove these viruses as rootkits reside in your system memory – not within the file storage component of your harddrive.

Macro Virus

A Macro Virus is a type of computer virus that is written in a macro language and embedded into a document or spreadsheet. When the user opens the infected document and enables macros, the virus executes its malicious code.

Unlike many other types of viruses, macro viruses deploy via software applications like Microsoft Word and Excel rather than executable files. Once activated, they can perform tasks like altering documents, sending files, or even downloading other types of malware.

By default, most word processing and spreadsheet computer programs disable macros and will prompt users to enable them if they are detected. Unless you are absolutely certain of the legitimacy of the file, do not enable macros.

Preventing Your Computer from Getting Viruses

Use a trusted antivirus software

Regularly updated antivirus software can detect and remove most viruses. While there are several good paid antivirus programs on the market, Windows computers now include an effective (and free) antivirus called Microsoft Defender.

While Mac computers offer robust built-in protection against viruses, they are not immune to viruses and will benefit from an antivirus.

Don’t click pop-up advertisements

Avoid clicking on pop-up ads as they may be laced with malware. Remember, if something seems too good to be true – it probably is.

Any messages indicating that you have won a free trip or some product should be treated with extreme skepticism.

Scan files that you download from file sharing sites

We recommend that you avoid downloading videos, music, games, or software programs from peer-to-peer (P2P) file sharing sites. However, if you do choose to do so, always scan the files with an updated antivirus before opening them.

Keep in mind that most cracked or pirated games include computer viruses including spyware and trojans.

Practice safe browsing habits

Be cautious when clicking links or downloading attachments. It doesn’t matter if you know the sender, all attachments should be treated with caution.

Keep your operating system updated

We get it. Downloading seemingly endless updates and the inevitable forced restarts that follow can get really annoying. However – these updates fix vulnerabilities and are an essential part of keeping your computer safe from hackers and cybercriminals.

Staying Vigilant in a Digital World

Awareness is your first line of defense in the battle against computer viruses. By recognizing the signs of infection and understanding how these digital pathogens operate, you are better equipped to stay safe.

In the ever-evolving landscape of cyber threats, staying educated and vigilant is not just an option, but a necessity for maintaining the health of your digital environment. For extra peace of mind, work with a professional computer security service and safeguard your system against viruses and malware.

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