What Are The Different Types Of Computer Viruses? (Updated)

May 25, 2020

5 min read

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In today’s digital age, computer viruses remain a persistent threat to our devices and data. These malicious programs come in various forms, each designed to disrupt, steal, or damage in unique ways.

From stealthy file infectors to adaptive polymorphic viruses, understanding the different types of computer viruses is crucial to protecting yourself and your systems. Here's a closer look at what computer viruses are, how they work, their different types, and how you can protect your devices from them.

What is a Computer Virus?

A computer virus is a type of malicious software (or malware) designed to disrupt, damage, or gain unauthorized access to computer systems. Named for its resemblance to biological viruses, it spreads by attaching its code to legitimate files or programs, replicating itself whenever those files or programs are executed.

Viruses can range from harmless pranks to destructive tools capable of stealing data, encrypting files, or rendering systems inoperable.

How Do Computer Viruses Work?

Viruses typically infiltrate systems through infected email attachments, compromised software downloads, removable media, or by exploiting unpatched system vulnerabilities. Once inside, they replicate by embedding their code into files or programs, ensuring they persist even if the original infection source is removed.

Many viruses remain dormant until triggered by specific conditions, such as opening an infected file, performing a particular action, or reaching a certain date.

When activated, viruses execute their “payload,” which can vary widely in impact. Some display harmless messages or images, while others disrupt systems by slowing them down or causing crashes. More malicious viruses may delete files, corrupt data, or steal sensitive information. They can spread further through shared networks, external devices, or by attaching themselves to outgoing emails and messages.

As cyber threats evolve, modern viruses have become more sophisticated, often using encryption or adaptive techniques to evade detection. Staying informed, practicing good cybersecurity hygiene, and keeping software updated are essential to protecting against these digital threats.

What Are the Common Types of Computer Viruses?

Computer viruses come in various forms, each with unique characteristics and methods of infection. Here are the types of computer viruses explained:

1. File-Infector Virus

A file-infector virus targets executable programs, such as those with .exe or .com extensions. When an infected program is executed, the virus activates and begins to spread by embedding itself into other files on the system.

Some file infectors overwrite the host file, rendering it unusable, while others modify the file's code to execute their payload. These viruses can lead to system crashes, corrupted data, or even complete hard drive failure. Their ability to piggyback on frequently used programs makes them particularly disruptive.

2. Macro Virus

Macro viruses exploit the built-in macro scripting languages found in applications like Microsoft Word or Excel. They are embedded within documents or templates and activate when the file is opened.

These viruses often spread through e-mail attachments, making them a common tool in phishing attacks. A macro virus might delete files, corrupt documents, or insert malicious scripts into other files. Their ease of distribution and potential to compromise widespread systems make them a persistent threat.

3. Browser Hijacker

Browser hijackers interfere with web browsers by altering settings such as the homepage, default search engine, or bookmarks. These viruses often redirect users to unwanted websites, typically filled with ads or malicious content.

In addition to being an annoyance, browser hijackers can expose users to further threats, including spyware and phishing schemes. They are commonly installed via bundled software downloads or fake browser extensions.

4. Web Scripting Virus

Web scripting viruses attack websites by injecting malicious scripts into their code. When users visit an infected site, the scripts can execute various harmful actions, such as stealing cookies, hijacking user sessions, or redirecting users to other malicious sites.

For instance, a web scripting virus might capture login credentials or post spam messages on behalf of the user. These viruses exploit vulnerabilities in website code or browsers and often spread through compromised links or ads.

5. Boot Sector Virus

Boot sector viruses target the critical boot sector of a storage device, such as a hard drive or USB stick. This sector contains essential code required to start the operating system. Once infected, the virus loads into memory during the startup process, often gaining control over the system. Historically common during the floppy disk era, boot sector viruses still pose a threat through USB drives and other external media. They can render systems unbootable, making recovery difficult without specialized tools.

6. Polymorphic Virus

Polymorphic viruses are particularly dangerous because of their ability to change their code with each infection. This adaptive behavior allows them to evade detection by traditional antivirus programs, which rely on static virus signatures.

These viruses often encrypt their payloads and modify their structure, making them difficult to analyze. They can perform a wide range of malicious actions, including data theft, system corruption, and the spread of additional malware.

7. Resident Virus

A resident virus embeds itself directly into a computer’s memory, enabling it to execute malicious actions independently of the original host file. Once installed, these viruses can corrupt files, interfere with system processes, and even replace legitimate programs with infected versions. Resident viruses are challenging to remove because they remain active in memory, even after the initial infection source is deleted.

8. Multipartite Virus

Multipartite viruses are among the most complex and infectious types of malware. They attack multiple parts of a system simultaneously, such as the memory, files, and boot sector. This multi-pronged approach allows them to spread quickly and remain resilient against removal efforts. For example, even if the infected files are cleaned, the virus may persist in the boot sector, re-infecting the system upon the next startup.

Related Article: What To Do When Your Computer Is Hacked?

How Can You Protect Your Device from Computer Viruses?

Protecting your device from computer viruses requires a combination of proactive habits and reliable security tools.

Start by installing the best antivirus software and keeping it updated to detect and neutralize threats. Regularly update your operating system and applications to patch vulnerabilities that viruses often exploit. Be cautious when opening e-mail attachments or clicking on links, especially from unknown sources, as these are common infection vectors. Avoid downloading software or files from untrusted websites and use a firewall to block unauthorized access to your network.

Additionally, backing up important data ensures you can recover files if an infection occurs. By staying vigilant and maintaining robust cybersecurity practices, you can significantly reduce the risk of falling victim to computer viruses.