Tips & Guides

The 10 Main Types of Computer Virus and How to Avoid Them

From macro virus to trojan horse, there are many different types of computer virus out there. Read our list of the most common ones & how to avoid them now.

Getting ill sucks. 

When you’re ill, everything seems hard work. Well, for a computer, it’s no different. 

Computer viruses – sometimes known as malware – come in many different forms. And there are lots of them – last year, these were an incredible 350,000 new pieces of malware (each one is a single piece of intrusive software) detected every single day.

From minor pests that slow your computer down to serious bugs that steal your data, here are the computer viruses you need to know about and what steps you can take to avoid them all.

Types of Computer Viruses

Viruses can find their way onto just about any device – from Windows PCs and Macs to iPhones and Androids. 

That’s right. Even phones are susceptible, particularly Android phones –  a recent report found that Android devices were responsible for 26% of all infected devices, including Windows PCs, IoT devices and iPhones.

And while Macs are often said to be more secure than PCs, latest data shows that this is actually not true, with more threats being now detected per endpoint on a Mac compared to a Windows computer. 

But either way, don’t worry. We’ve summed up the most common computer viruses and how you can avoid them below:

10 main types of computer virus - TechBuddy Infographic

Macro Virus 

This type of computer virus is normally found in Microsoft Office programs. Word and Excel files are favorite places for macro viruses to embed themselves. Like most other viruses (except spacefillers – more on these later) macro viruses increase the size of files when they infect them, as they attach their own code. Once a macro virus infects a file, it can easily spread to other computers when that file is shared, for example via email.

Boot Sector Virus

Much like beepers and Tamagotchis, boot sector viruses are terrible little things that were big in the 90s. One of the oldest types of viruses, boot sector viruses go straight for the core of your computer, affecting the startup or ‘boot’ process. Back in the day, these viruses were spread through floppy disks. Nowadays, they attach themselves to emails or USB sticks. If your computer catches one of these, you’ll need an expert to carry out a full system reformat (Windows, Mac). 

Trojan Horses

Taking their name from the huge wooden horse in which the Greeks hid to get inside the ancient city of Troy, these are among the sneakiest of computer viruses. Used by cyber-criminals, Trojan horses are disguised as normal programs, tempting you to install them on your computer. Once installed, the viruses gain access to your computer's files and capture your private data – think passwords and online banking information. This can then be used by hackers to make online purchases with your bank account or expose your private information.

Overwrite Virus


When it comes to pests, these take first prize. Overwrite viruses typically take over a file and wipe the original code without you even knowing it. Once deleted, the original files cannot be recovered and the data is lost. They often spread through emails via attachments or through file downloads on the internet, so always scan files with an anti-virus software before downloading and opening them. This will help you detect these viruses before they even have a chance to cause problems.  

Browser Hijacker

The digital equivalent of a crooked cold-caller salesman, browser hijackers take over your internet searches and redirect you to pages you didn’t even want to visit. While not as harmful as other types of viruses – they trick you rather than steal from you – browser hijackers are still an annoying problem since they significantly lower your UX when surfing the internet. If you experience lots of random pop-up adverts or your usual homepage browser has changed without you telling it to, chances are you’ve got a browser hijacker. Always scan email attachments before opening and avoid downloading files from suspicious websites to avoid browser hijackers.

Web Scripting Virus

This is one for the modern age. Web scripting viruses are very clever little bugs that blend into the background of popular websites – usually social media platforms. They disguise themselves as normal links, tempting you to click on them. Then, like a greedy schoolyard bully, they steal your cookies. Ok, different cookies – we’re talking the kind of cookies that store your information. Still, web scripting viruses definitely shouldn’t be taken lightly – they can send spam to your system and damage your data, and can spread faster than most viruses.   

Polymorphic Virus

polymorphic virus

This is one sly virus. Like a chameleon changing its color for every situation, a polymorphic virus modifies whenever it replicates. This makes it hard for most anti-virus programs to keep up. Once it’s found its way onto your computer – usually through an email attachment or a download from a suspicious website – it has free reign to delete your files, steal your data, and generally sabotage your system. The bad news is these shape-shifting charlatans are on the rise. The good news is that the top antivirus programs are starting to adapt alongside them, using more sophisticated scanning techniques to catch these chameleons in the act.  

Resident Virus

One of the most common types of virus you’ll (hopefully not) come across, these sneaky little squatters find their way into your computer’s memory, completely uninvited, and make themselves at home. Just think of your old flatmate’s annoying friend who would invite themself over every night and steal your Ben and Jerry’s from the fridge. Resident viruses can come from email attachments, infected downloads or shared files and are then activated whenever your computer performs a specific action and can even attach themselves to anti-virus software, scamming the very thing that’s tasked with bringing it down. The best solution? Get an expert involved.

Multipartite Virus

Sometimes called ‘multi-part viruses’ these flexible fiends are on the rise. While most viruses either attack a computer’s central boot sector or through its files, a multipartite can do both. A versatile virus is hard to prevent, which explains the rapid growth rate of multipartite in recent years. They usually spread through .exe files – so programs like Word and Excel. How do you know if your computer is infected with a multipartite virus? Well, these viruses eat up your virtual memory like nothing else, so expect lots of ‘your computer has low virtual memory’ messages and a sudden slowing down of your computer.

Spacefiller Virus 

Also known as ‘‘cavity viruses’, spacefiller viruses find the empty spaces in a program code and climb right in by adding their own code. This way, they don’t alter the size of files (as other viruses do), which makes them very hard to detect. Most antivirus programs find it hard to catch spacefillers, but there are a few manual virus-hunting tools that tech experts use to root them out. Thankfully, they’re not only hard to detect, but they’re also hard to create and there aren’t many file types that they can attach to. This makes spacefiller viruses very rare. 

BuddyCompany Tips on Preventing and Dealing With Viruses 

How to Avoid and Lessen the Impact of Viruses

Now that you know about the different types of computer viruses, here are a few tips on how to avoid letting them in.

Use a firewall

A firewall is your computer’s first line of defense. While an antivirus program (more on that later) is active in your computer, detecting and neutralizing viruses, a firewall sits between your computer and the internet, swatting them away. Your computer normally comes with a pre-installed firewall – make sure it’s enabled

Don’t click on suspicious links or pop-ups

The first one should be the most obvious. But so many people get suckered into clicking on dubious links on the internet. Ok, so we’ve all been tempted to click on a ‘12 Hollywood Actors Who Have Really Let Themselves Go’ link – especially when number 9 will “literally make your jaw drop.” Sometimes we all have to learn the hard way. But the golden rule is, if you don’t know or trust the website, proceed with caution. And always use a pop-up blocker.

Don’t open email attachments or links you aren’t sure about

suspicious email with a computer virus
Don’t click on links that come from suspicious looking emails and senders

Emails are one of the main ways computer viruses spread. When a computer is infected, viruses ‘blast email’ all the contacts on that computer. So, if an attachment seems a bit suspicious - if it’s got a strange file name, there are typos in the email, the content of the email seems odd or the sender’s email address looks strange, for instance - don’t open it. Even if it’s from someone you know.

Backup your files

Just imagine losing your most valued documents, photos, videos, etc. Almost unthinkable, right? That’s why, in the event that a virus gets through, it makes sense to have your data backed up. Make a copy of everything and store it on an external hard drive, as well as another computer, if possible.

Update your operating system

You know those annoying little update messages that pop up at the most inconvenient time? Well, it’s time to stop ignoring them. Whether you’re on a Mac or a PC, it’s crucial to keep your operating system up to date. Developers are constantly adding new improvements, many of which will help keep your computer free from viruses.

How to Detect Viruses

how to detect a computer virus

If you suspect you might have a computer virus, here’s how you can detect it.

Install a reliable antivirus program

A surprisingly large number of people don’t use antivirus programs. Whether it’s McAfee, Norton, Kaspersky, Bitdefender, or another top program, having a quality antivirus program is your computer’s second line of defense against viruses. It’s also a prerequisite for virus detection.

Run regular scheduled scans with your antivirus program

Having the program is all well and good. But it means nothing if you don’t run virus scans. Ideally, you should run a scan once a week, every two weeks or whenever you think your computer might have caught a virus. You can set antivirus programs to scan automatically when it suits you – for instance, a specific time of day when you know you won’t be using your computer. Once a virus is identified, your antivirus program can also often help you remove it.

Call a Buddy!

While antivirus software, firewalls, and being switched on to the typical tricks of the trade are all important, viruses are becoming harder to detect and harder to prevent. 

So, if you’re not sure what firewall or antivirus program to choose, want to know the best way to protect your computer, or need to get rid of a virus, don’t worry… BuddyCompany is here to help! 

Contact us and get connected with a tech-savvy expert today.

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