Computer Virus

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Computer Virus

What is a Computer Virus?

A computer virus is a malicious program designed to:

  • Damage data

  • Corrupt files

  • Slow down the system

  • Spread from one computer to another

It attaches itself to programs, files, or the operating system and spreads when the infected file or program is executed.

Characteristics of a Computer Virus

  • Small malicious program

  • Reproduces itself (self-replicates)

  • Can damage or delete data

  • Spreads through USB, email, internet, apps

  • Reduces system performance

  • Works without user permission

How Viruses Spread?

  • Infected USB drives

  • Downloading infected software

  • Email attachments

  • Visiting harmful websites

  • File sharing networks

Types of Computer Viruses

Below are the major types explained clearly:

1. File Infector Virus

Infects .exe, .com, and other executable files.
Activates when the infected file is opened.

Examples:

  • Jerusalem Virus

  • Cascade Virus

2. Boot Sector Virus

Infects the boot sector or master boot record (MBR) of a hard disk or USB drive.
Loads automatically when the computer starts.

Examples:

  • Michelangelo

  • Stoned Virus

3. Macro Virus

Written using macro languages (like in MS Word or Excel).
Infects documents and spreadsheets.

Examples:

  • Melissa Virus

  • DMV Virus

4. Polymorphic Virus

Changes its code and appearance every time it infects a system, making it hard to detect.

Example:

  • Satan Bug

  • Vundo Virus

5. Metamorphic Virus

Rewrites its own code completely, making it even harder to detect compared to polymorphic viruses.

Example:

  • Zmist Virus

6. Resident Virus

Hides in the RAM and infects files while they are being processed by the system.

Examples:

  • Meve

  • CMJ Virus

7. Non-Resident Virus

Does not stay in memory.
Spreads only when the infected program is executed.

8. Multipartite Virus

Infects multiple parts of a system at the same time — files, boot sector, memory.

Example:

  • Ghostball Virus

9. Web Scripting Virus

Spreads through web pages, harmful scripts, and unsafe websites.

Example:

  • JS.Fortnight

10. Worms (Self-Spreading)

A worm is not exactly a virus but is a self-replicating malware that spreads over networks automatically.

Examples:

  • ILOVEYOU Worm

  • MyDoom

  • WannaCry

Effects of Computer Viruses

  • Slow performance

  • Data corruption

  • Automatic system restarts

  • Frequent crashes

  • Unwanted pop-up messages

  • Loss of personal data

  • Stealing passwords

Protection Against Viruses

  • Install antivirus software

  • Keep system updated

  • Avoid unknown email attachments

  • Use safe websites

  • Scan USB drives

  • Do not download cracked software

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