1. What is a Computer Virus?
A computer virus is a type of malicious software (malware) that, when executed, replicates itself by inserting its code into other programs or files. When these infected files are opened, the virus spreads to other systems, causing damage such as data corruption, system slowdowns, unauthorized access, or total system failure.
2. How Does a Computer Virus Work?
A virus typically follows these steps:
- Infection: The virus attaches itself to a file or program.
- Activation: When the infected file is opened, the virus executes its code.
- Replication: The virus spreads to other files, programs, or systems.
- Payload Execution: The virus performs harmful activities such as deleting files, stealing data, or slowing down the system.
3. Common Ways Computer Viruses Spread
- Email Attachments – Malicious files attached to phishing emails.
- Infected Software Downloads – Downloading software from untrusted sources.
- Removable Media (USB, External HDDs) – Carrying infected files between computers.
- Malicious Websites – Visiting compromised or fake websites.
- P2P File Sharing & Torrents – Downloading infected files.
4. Types of Computer Viruses
Computer viruses come in different forms based on how they spread and affect the system.
A) Based on Infection Method
| Type | Description | Example |
|---|---|---|
| File Infector Virus | Attaches itself to executable files (.exe, .dll) and spreads when executed. | CIH (Chernobyl) |
| Boot Sector Virus | Infects the boot sector of storage devices, preventing system startup. | Michelangelo |
| Multipartite Virus | Combines different infection methods, affecting both files and boot sectors. | Invader |
| Macro Virus | Targets macros in Microsoft Office files (Word, Excel). | Melissa, Concept |
| Resident Virus | Hides in system memory and infects files without execution. | Randex, CMJ |
| Direct Action Virus | Activates when a specific infected file is executed but does not stay in memory. | Vienna Virus |
B) Based on Functionality
| Type | Description | Example |
|---|---|---|
| Polymorphic Virus | Changes its code to avoid detection by antivirus software. | Storm Worm, Marburg |
| Metamorphic Virus | Completely rewrites itself to evade detection. | Simile |
| Overwrite Virus | Overwrites file content, making data unrecoverable. | Trj.Reboot |
| Stealth Virus | Hides from antivirus programs by modifying system functions. | Frodo, Whale |
| Ransomware | Encrypts files and demands payment to restore access. | WannaCry, Ryuk |
C) Other Notable Types
| Type | Description | Example |
|---|---|---|
| Worms | Self-replicating malware that spreads without user action. | ILOVEYOU, Morris Worm |
| Trojan Horse | Disguised as legitimate software to trick users into installing it. | Zeus, Emotet |
| Spyware | Secretly monitors user activities and steals sensitive information. | DarkHotel, Pegasus |
| Adware | Displays unwanted ads and collects browsing data. | Fireball, Gator |
5. Effects of a Computer Virus
- Data Corruption – Deletes or modifies files.
- System Performance Issues – Slows down computers and crashes programs.
- Unauthorized Access – Hackers gain control of infected systems.
- Network Spread – Spreads across networks, affecting multiple devices.
- Financial Loss – Causes downtime, data theft, and ransom demands.
6. Prevention and Protection Against Viruses
✅ Best Practices to Avoid Viruses
- Use Reliable Antivirus Software – Keep it updated.
- Avoid Suspicious Links & Email Attachments – Do not open unknown files.
- Keep Software Updated – Install security patches regularly.
- Use Firewalls – Prevents unauthorized network access.
- Backup Important Data – Protects against data loss from ransomware attacks.
- Disable Macros in Documents – Prevents macro-based viruses.
7. Real-World Examples of Computer Viruses
🔹 ILOVEYOU (2000)
- Spread via email attachments, overwriting files and stealing passwords.
- Caused $15 billion in damages globally.
🔹 WannaCry (2017)
- A ransomware attack that locked Windows computers.
- Exploited a Microsoft Windows vulnerability, affecting 200,000+ systems worldwide.
🔹 Mydoom (2004)
- The fastest-spreading email worm in history.
- Used infected computers to launch DDoS (Distributed Denial of Service) attacks.
Conclusion
A computer virus is a major cybersecurity threat that can cause data loss, financial damage, and system crashes. Understanding its types, effects, and prevention methods helps individuals and businesses stay protected.
