The worst computer viruses can destroy anything from a single program to your entire computer system, eradicating important files, putting personal data at risk and requiring a full reformat of your hard drive to get things working again. If you've spent a lot of money on one of the best home computers (opens in new tab) or best laptops (opens in new tab) you can afford, you need to know how to protect them, and what to protect them against.
There are well over 100,000 known computer viruses and although only a small percentage exist “in the wild” they remain widespread, posing a serious threat to your computer. Viruses are also used by hackers to gain access to your system and steal personal information including bank details and passwords. So it’s certainly important that you know about the different types of virus that can infect and affect your personal computer. This guide explains ten of the worst types of past and recent computer viruses and provides simple solutions for avoiding them. When you’ve finished, be sure to read about the best antivirus software (opens in new tab) to ensure you have the best possible protection.
1. Browser hijacker
Imagine typing in an internet address and automatically bouncing through several different sites. When this happens, a browser hijacker is usually responsible for the incident. Unfortunately, hijackers are often attached to appealing toolbars, programs and other free downloads you choose. Thankfully, a good security program can detect nearly all of these.
2. Stealth virus
As the name suggests, Stealth Viruses can stay undetected for an extended period of time and conceal the changes they make to an infected system. Like other malware, they hijack a wide range of system tasks and can adversely affect performance, concealing themselves from antivirus programs by copying to another location and replacing themselves with a clean file. They can be tricky to eradicate, but a high-end solution such as Kaspersky Internet Security (opens in new tab) can detect and remove them.
3. File infector
One of the most common types of computer virus is a file infector. These viruses attach to host files (.exe), which means they usually stick to files you use often. The virus will run any time you open or run the file, and it can even take over the file completely. The best way to combat a file infector virus is with a good antivirus program like Bitdefender (opens in new tab) or Norton 360 Antivirus (opens in new tab).
4. Macro virus
This is another type of file-based virus which attaches to files like Microsoft Excel and Word documents, along with other applications that support macros (the famous Melissa virus being a well known example). A Macro virus will not only infect the user, but also his/her friends and colleagues by emailing itself to their contact list. A trusted antivirus solution will scan incoming mails, but it’s also good practice not to open unsolicited attachments from strangers or suspicious-looking emails from friends.
5. Multipartite virus
A very infectious type of virus that uses multiple methods to spread. They can perform unauthorized actions in the operating system and have the ability to infect both executable files and the boot sector. A telltale sign may be constant error messages warning of low virtual memory, as multipartite viruses consume memory while spreading to executable files.
6. Polymorphic Virus
A particularly nasty type of virus that is hard to detect due to their ability to encrypt and change their coding every time they infect a system. So how can you protect against them? Kaspersky Internet Security (opens in new tab) advise; “one of the simplest ways to protect against adaptive code is to have the right type of security solution in place. A high-quality antivirus solution has the ability to deploy a far more comprehensive range of tools and algorithms to recognize and deal with a wider range of threats.” It also pays to employ vigilance and good judgement when downloading email attachments and spotting websites that may be compromised.
7. Direct Action Virus
Direct Action Viruses aren’t as common these days, although they were capable of causing a great deal of damage in the past. As the name suggests, they would only activate when the file or program they were attached to was executed, ceasing to run once the program was terminated. Any good security solution will detect and remove this type of virus, including free services like Avast Free Antivirus (opens in new tab).
8. FAT Virus
FAT viruses ruin your file allocation system, which is where information about files, and where to find them, exists. It will destroy files and entire directories.
9. Web Scripting Virus
These viruses live within the coding used to construct websites and can either be included deliberately by malicious sites, or unknowingly on sites infected by hackers. Either way it pays to be cautious about the sites you visit, as web scripting viruses carry malicious codes that can infect your computer when you click links or watch videos. In our tests F-Secure (opens in new tab) did an excellent job in blocking sites we knew had either a malicious link or virus download.
10. Memory Resident Virus
This form of computer virus is very destructive. It embeds itself in the computer's memory to carry out operations. This means whenever you run your operating system, the virus is working. It has varying effects, but it will clear up space on your computer for its own use by corrupting and deleting your files.
Windows has long been the operating system most targeted by hackers and viruses but there are also threats aimed at the Mac OS, so Apple users shouldn’t consider themselves immune. Also, it’s not just your desktop that’s at risk. Although there’s technically no smartphone malware that will replicate itself to spread like a PC virus can, there is a growing amount aimed at Android devices that can steal passwords and other personal data. Thankfully, many of the security packages listed in our best internet security software (opens in new tab) guide have all you need to stay protected, no matter what device you're using. This software will also scan downloads and sites in advance, offer malware detection and removal and block outside attempts to access your desktop or mobile device. The peace of mind they offer is worth every cent.