Types of computer viruses explained

Software viruses are one of the biggest concerns and account for over half of the threats to your PC. Protecting it against a virus will help to ensure a smooth-running computer, which is why it helps to have all the information to hand when it comes to virus-related issues.

In this guide, we’re covering everything you need to know about computer viruses and how you can protect your PC against them.

What is a computer virus?

A virus is software or coding that's harmful and infects programs on your computer. By opening an infected file, you activate the virus, which can damage your PC and affect its files, internet security and the computer itself.

Viruses can travel from PC to PC through file downloads, email attachments and compromised software. It lies dormant until the file is opened and the software or attachment is downloaded. At this point, the virus infects your computer.

The more these files are shared between computers, the higher the chance of them spreading. Viruses can steal your passwords, corrupt files, spam your emails and slow down your computer.

What causes computer viruses?

Most computer viruses only come into effect when the user activates them. This might include downloading a file online without realising there is a virus attached, or inserting hardware into your PC. Primary viruses causes include:

• Downloading infected software
• Opening email attachments that contain a virus
• Inserting a disc, floppy disk on older computers, or thumb drives with a virus attached
• Accepting downloads without reading the fine print (eg, clicking on the “add additional software” pop-up or opening a link that suggests your computer might be infected)
• Visiting harmful websites with suspicious links
• Not updating your computer to the latest software
• Illegally downloading music, movies and TV shows
• Not having antivirus spyware scanners

What are the common types of virus?

Unfortunately, computers are susceptible to many different viruses. Some of the most common ones are:

• Resident virus – attacks the computer’s RAM and interferes with your system operations. A resident virus can also attach itself to anti-virus software files.
• Network virus – replicating themselves through shared resources, network viruses travel through network connections.
• Browser hijacker – a browser hijacker infects your internet browser and redirects you to harmful websites.
• File infector – programs and system files can be damaged by a file infector virus, which targets .exe files.
• Multipartite virus – by performing unauthorised actions on your PC, multipartite viruses target your entire computer system including programs, folders and operating systems.

There are other virus-related issues that can cause your computer all sorts of problems, such as malware, spyware, Trojan horses and worms.

What is malware?

Short for malicious software, malware is a type of computer program designed to infect a PC in varying forms. It can potentially contain viruses, worms, spyware and Trojans, all of which can harm your PC and even stop it from working.

Computer viruses are one of the most common types of malware, which spreads by making copies of itself. Essentially, it’s a code designed to disrupt, disable and take control of your computer system and is typically hidden in a file or disguised as an app.

What is spyware?

Spyware is a form of malware that gathers information about your computer. It can carry high-level security and privacy risks, taking data about your PC and sharing it with a third party. Spyware usually installs itself on a computer without your knowledge, making it harder to detect.

What is a Trojan horse?

Trojan horses are a type of code or software that take control of your computer and generally cause damage in some capacity, stealing information, damaging the PC or disrupting its performance. A Trojan horse acts as a legitimate file and tricks you into downloading it.

What is a computer worm?

A computer worm copies itself from computer to computer. It doesn’t need to attach to a software or program to cause damage and can replicate itself without any human interaction. Computer worms are typically spread through software vulnerabilities.

What are the signs of a computer virus?

Identifying the signs of a computer virus isn’t easy, but there are a few signifiers that indicate your PC could have one. These include common signs like your computer suddenly running slowly, or a lack of space on your hard drive even though you haven’t downloaded anything.

Suspicious activity, such as your computer doing something when no programs are running, is a red herring, as are unwanted pop-ups or toolbars. If you suddenly find that several emails have been sent out in your name, there’s every chance that it could be a virus.

An overworked hard drive, which spins excessively or conutines to make noise could also point to a serious virus-related issue. While constant crashes and error messages on your PC indicate that the computer could be infected.

What is antivirus software? 

With so many viruses potentially posing a problem to your computer, it's vital that PC owners have something in place to mitigate the risks. Enter antivirus software, which helps protect your computer against viruses and cybercriminals.

Antivirus software trawls through data on your computer and on the web, searching for potential risks and threats while monitoring the behaviour of all your programs. Without antivirus software, you increase the risks of exposing your computer to a virus and the evolving level of cyber threats.

Software such as Norton™ 360 Deluxe 5 Devices offers powerful protection to your devices and online privacy, and can protect up to 5 PCs, Mac®, smartphones or tablets.