10 Types of Common Computer Viruses

Viruses are among the most recognised and destructive types of malware, known for their ability to replicate and spread throughout a system. Unlike other types of malware that act stealthily or require user permission, viruses often infect by embedding themselves into legitimate files, causing system slowdowns, data loss, and even allowing access to unauthorised users. While “virus” is sometimes used interchangeably with “malware,” it’s a specific kind of malware that has its unique way of disrupting systems. Understanding the key types of computer viruses can help you recognise potential threats and improve your security strategy.

The Main Type of Computer Virus

1. File Infector Viruses

File infector viruses are a classic type of malware that attach themselves to executable files, typically ones with extensions like .exe or .com. When an infected file is opened, the virus spreads, infecting other files within the system. These viruses are known for their ability to hide within frequently used files, making them harder to detect. Some even modify their code each time they replicate, bypassing traditional antivirus software. If left unchecked, they can corrupt files, causing data loss or forcing users to reinstall their operating systems.

2. Macro Viruses

Macro viruses target applications that rely on macros, like Microsoft Word and Excel. These viruses embed themselves within documents and execute malicious code whenever the document is opened. Because macro viruses can spread through seemingly harmless files like spreadsheets and reports, they can quickly infect multiple systems via shared documents or email attachments. Although they’re simple in design, their capacity to disrupt office environments is significant, as they can compromise sensitive information or corrupt important files.

3. Boot Sector Viruses

Boot sector viruses are a particularly dangerous breed, attacking the boot sector or master boot record (MBR) of a hard drive. By embedding themselves at the startup level, boot sector viruses activate whenever the computer is turned on, often before the operating system loads. They spread through infected media such as USB drives and network connections. Because boot sector viruses operate at such a fundamental level, they are challenging to remove, sometimes necessitating a complete system reformat or hard drive replacement.

4. Polymorphic Viruses

Polymorphic viruses are some of the most elusive types of malware due to their ability to change their code with each new infection. This mutation allows them to avoid detection by antivirus software that relies on specific signatures to identify threats. Polymorphic viruses retain their core malicious functionality while altering their appearance, making them extremely difficult to detect and remove. Due to their adaptive nature, they require advanced, multi-layered security approaches to manage effectively.

5. Resident Viruses

Unlike non-resident viruses, which remain dormant until their host file is opened, resident viruses embed themselves in a computer’s memory (RAM), allowing them to execute even after the infected file is closed. This enables resident viruses to activate whenever specific conditions are met, such as when another file is accessed. These viruses are known for causing unpredictable slowdowns, frequent crashes, and other performance issues. Because they reside in memory, they’re often challenging to detect and remove without advanced antivirus software.

6. Multipartite Viruses

Multipartite viruses are capable of infecting multiple areas of a computer, such as the boot sector and system files, making them highly adaptable and dangerous. By targeting various parts of the system simultaneously, multipartite viruses can spread quickly and cause extensive damage. Even if one component is removed, the virus can remain active in another area, making it notoriously difficult to eliminate. Effective removal of multipartite viruses requires a combination of tools that target both boot sector and file infections.

7. Web Scripting Viruses

Web scripting viruses use malicious code embedded in web pages to infect a user’s browser. Often, these viruses exploit vulnerabilities in popular browsers or website plugins to execute their code. Web scripting viruses are especially effective on high-traffic websites or social media platforms, allowing them to spread rapidly. They can redirect users to malicious sites, steal login credentials, or install other types of malware without the user’s knowledge. Maintaining browser security settings and avoiding suspicious sites can help prevent these infections.

8. Direct Action Viruses

Direct action viruses, sometimes known as non-resident viruses, only activate when a specific condition is met—typically when an infected file is opened. They don’t remain in the computer’s memory, so they only cause damage during particular actions, such as file access or system startup. While their limited activity makes them somewhat easier to remove, direct-action viruses can still interfere with system performance and cause data loss, especially if they infect critical files.

9. Overwrite Viruses

Overwrite viruses are highly destructive, overwriting files with their malicious code and rendering the original content irretrievable. These viruses are hazardous for businesses with valuable data, as they permanently alter or destroy files without the possibility of recovery. Unlike other types of malware that might infect multiple files across a system, overwrite viruses tend to focus on the data they overwrite, making early detection and removal crucial to prevent widespread data loss.

10. Ransomware

Ransomware has become one of the most disruptive types of malware in recent years, especially for organisations. Unlike other viruses that replicate or simply corrupt files, ransomware encrypts files and locks users out of their data, demanding a ransom for its release. There are various forms of ransomware, such as locker ransomware, which locks users out of their devices, and crypto-ransomware, which encrypts specific files. Preventing ransomware requires consistent data backups, network security best practices, and user education to recognise phishing and other common infection methods.

Strengthening Your Defences Against Computer Viruses

While these viruses differ in how they operate and spread, protecting against them involves a few essential practices. Here’s how you can secure your systems against these threats:

• Regular Updates and Patching: Keeping your operating system and software up to date ensures that vulnerabilities are patched, reducing your exposure to known exploits.
• Use Antivirus Software: Antivirus programs are designed to detect and block a wide range of viruses and malware, providing real-time protection for your devices.
• Educate Users on Safe Practices: Many viruses rely on user actions, like clicking on malicious links or opening infected attachments. Educating the team on identifying and avoiding potential threats can help reduce infections.
• Backup Your Data Regularly: Frequent backups protect against data loss from viruses like ransomware and overwrite viruses, ensuring that you can recover your files even if an attack occurs.

Reach Out to IT for Business for Robust Cybersecurity 

With cyber threats evolving daily, having a proactive approach to cybersecurity is essential. IT for Business provides expert managed security services to ensure real-time protection against digital threats. From security assessment to virus protection, we’re here to support your business every step of the way. Contact us today to learn more about securing your systems and safeguarding your digital assets.