Types of Computer Viruses You Should Know About

Key Takeaways

Computer viruses are malicious programs designed to disrupt systems, steal data, or cause harm. They come in various forms, such as worms, trojans, ransomware, and spyware, each with unique functions. Preventive measures like using antivirus software, updating systems, and practicing safe browsing are essential.

Computer viruses are almost the same as human viruses.

There are various types of computer viruses affect computer or laptop as the human virus affects us. Once a virus enters your PC or computer.

The virus spreads from one program to another.

Types of Computer Viruses

1. Macro Viruses

Macro viruses are written in programming languages like VBA (Visual Basic for Applications) used in applications such as Microsoft Word and Excel.

These viruses exploit the macro functionalities to automate malicious actions.

How They Spread?

They spread through infected files, especially email attachments or downloaded documents. When the file is opened, the macro code automatically executes tasks like replicating the virus or corrupting data.

Example: The Melissa Virus

The Melissa virus caused extensive damage by infecting email systems and spreading rapidly through mass-mailing. The outbreak disrupted global email systems and caused financial losses of over $80 million.

2. Web Scripting Viruses

Web scripting viruses exploit vulnerabilities in web browsers, using scripting languages such as JavaScript or VBScript to execute harmful actions.

Attack Methods

These viruses are often injected into web pages, targeting users who visit infected sites.

Non-persistent versions disappear when the browser is closed, while persistent ones remain active even afterward.

Impact: XSS Attacks

Cross-site scripting (XSS) attacks inject malicious scripts into trusted websites. These scripts steal sensitive data like cookies or user credentials, often leading to identity theft or unauthorized access.

3. Browser Hijacker Viruses

Browser hijacker viruses modify web browser settings without user consent.

They often install as part of bundled software downloads or through deceptive ads.

Effects on Browsers

These viruses redirect searches, change the homepage, or install unwanted toolbars. They may also track browsing activity to deliver targeted ads, compromising user privacy.

Example: CoolWebSearch

CoolWebSearch is notorious for its persistence, often reinstalling itself after removal attempts, making it particularly challenging to eliminate.

4. Resident Viruses

Resident viruses embed themselves in a computer’s memory (RAM) and remain active even after the host program ends.

Fast vs. Slow Infectors

Fast infectors act immediately when a file is executed, spreading quickly across the system. Slow infectors trigger only when files are modified, making detection more difficult.

Example: Jerusalem Virus

The Jerusalem virus caused widespread disruption by deleting files every Friday the 13th, showcasing its destructive capabilities.

5. File-Infecting Viruses

File-infecting viruses attach themselves to executable files such as .exe or .sys, executing malicious code when the infected file is run.

Behavior

These viruses modify file contents, create new infected files, or corrupt existing ones. Some may allow the original program to run to avoid immediate detection.

Example: Cascade Virus

The Cascade virus displayed falling characters on infected screens while damaging system files.

6. Overwrite Viruses

Overwrite viruses destroy files by replacing their original content with malicious code, making data recovery impossible.

These viruses often target critical system files, causing operational failures or rendering the system unusable.

Example: Trivial.88.D

The Trivial.88.D virus showcased how a simple virus could cause extensive damage by overwriting vital system files.

7. Boot Record Viruses

Boot record viruses target the Master Boot Record (MBR) or boot sector of storage devices.

Pre-OS Activation

They activate before the operating system loads, making them highly dangerous. They can prevent system startup, corrupt disk structures, or create backdoor access for further exploitation.

Example: Michelangelo Virus

The Michelangelo virus activated annually on March 6, deleting data and damaging systems on a massive scale.

8. Multipartite Viruses

Multipartite viruses use multiple infection methods, typically combining boot sector and file infection techniques.

Dual Infection Strategies

These viruses create multiple infection points within the system, making them harder to remove completely.

Example: Tequila Virus

The Tequila virus demonstrated how combining boot sector and file infection capabilities helped evade detection and removal efforts.

9. Direct Action Viruses

Direct action viruses execute their payload immediately upon activation and deactivate afterward.

These viruses target specific file types, performing their infection routine as soon as the file is accessed.

Example: Vienna Virus

The Vienna virus infected files during execution without leaving traces in system memory.

10. Cavity Viruses

Cavity viruses exploit unused space within files to insert malicious code without increasing the file’s size.

By keeping the file size unchanged, cavity viruses remain hidden for extended periods. They target executable files for long-term system compromise.

Example: CIH (Chernobyl) Virus

The CIH virus caused extensive data loss by overwriting critical system files and destroying BIOS firmware.

11. Metamorphic Viruses

Metamorphic viruses rewrite their code entirely during replication, making each version unique.

These viruses adapt by changing their structure and functionality while maintaining their malicious intent.

Example: MetaPHOR Virus

The MetaPHOR virus is one of the most sophisticated examples, evading detection and removal through code transformation.

12. Cluster Viruses

Cluster viruses modify directory entries to redirect programs to malicious code instead of their actual files.

These viruses alter how the system accesses files without directly changing the file itself.

Example: Dir-2 Virus

The Dir-2 virus exploited directory structures to cause widespread disruption without altering host files.

13. Network Viruses

Network viruses spread through network protocols and services, often exploiting vulnerabilities to propagate across systems.

They use shared resources, email protocols, or unpatched software to infect connected systems.

Example: Nimda Virus

The Nimda virus used multiple vectors, including email and shared directories, to infect systems globally.

14. Stealth Viruses

Stealth viruses use advanced techniques to hide their presence from antivirus programs and system administrators.

These viruses intercept system calls and return false information, hiding file size changes or boot sector modifications.

Example: Brain Virus

The Brain virus was one of the earliest stealth viruses, using innovative methods to evade detection while infecting floppy disks and early PCs.

Also, Read Database Security Top 10 Ways

Comparison of Computer Viruses

Virus Type
Characteristics
Effects
Example
Macro Viruses
Written in macro languages (e.g., VBA) used in applications.
Spread through email attachments, automating malicious actions.
Melissa Virus
Web Scripting Viruses
Exploit vulnerabilities in browsers using scripting languages.
Steal cookies, inject code, and modify webpages.
Cross-Site Scripting (XSS)
Browser Hijacker Viruses
Modify browser settings via bundled downloads or ads.
Redirect searches, install unwanted toolbars, track users.
CoolWebSearch
Resident Viruses
Reside in system memory (RAM) and remain active.
Corrupt data, disrupt operations, infect accessed files.
Jerusalem Virus
File-Infecting Viruses
Attach to executable files, running malicious code.
Modify or corrupt files, create infected files.
Cascade Virus
Overwrite Viruses
Replace file content with malicious code, making recovery impossible.
Destroy critical files, disrupt operations, render systems unusable.
Trivial.88.D
Boot Record Viruses
Infect the Master Boot Record (MBR) or boot sector of devices.
Corrupt disk structures, prevent system startup, enable backdoor access.
Michelangelo Virus
Multipartite Viruses
Use multiple methods, targeting both boot sectors and files.
Create multiple infection points, making removal complex.
Tequila Virus
Direct Action Viruses
Activate immediately when executed, then deactivate.
Infect specific file types without remaining in memory.
Vienna Virus
Cavity Viruses
Exploit unused file space, injecting code without increasing file size.
Evade detection while compromising system files.
CIH (Chernobyl) Virus
Metamorphic Viruses
Rewrite their code with each replication, making versions unique.
Evade antivirus software through constant transformation.
MetaPHOR Virus
Cluster Viruses
Modify directory entries to redirect programs to malicious code.
Disrupt program access without directly modifying files.
Dir-2 Virus
Network Viruses
Spread through network protocols and services.
Infect systems via email, shared directories, or network resources.
Nimda Virus
Stealth Viruses
Use techniques to hide from detection, such as intercepting system calls.
Conceal changes in file sizes, boot sectors, or system files.
Brain Virus

FAQs

What is the most dangerous type of computer virus?

Ransomware is often considered the most dangerous because it encrypts critical data and demands payment, causing significant financial and operational disruptions.

How can I tell if my computer has a virus?

Signs include slow performance, frequent crashes, excessive pop-ups, and unauthorized access to files or accounts.

Can antivirus software stop all viruses?

While antivirus software is essential, it may not detect new or highly sophisticated viruses. Regular updates and additional security measures are necessary.

Is it safe to open email attachments?

Only open email attachments from trusted sources. Scan attachments with antivirus software before opening.

What should I do if my computer is infected?

  • Disconnect from the internet to prevent further spread.
  • Run a full system scan with antivirus software.
  • Seek professional assistance if the issue persists.

Conclusion

Computer viruses are a persistent threat in the digital landscape.

By understanding their types and adopting preventive measures, individuals and organizations can safeguard their systems against infections.

Regular updates, robust security software, and informed practices are key to combating these malicious programs effectively.

Also Read DoS vs DDoS: Which Attack is More Dangerous?

Author

Allen

Allen is a tech expert focused on simplifying complex technology for everyday users. With expertise in computer hardware, networking, and software, he offers practical advice and detailed guides. His clear communication makes him a valuable resource for both tech enthusiasts and novices.

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