Table of Contents
Introduction
A computer virus is a type of malicious software (malware) that is designed to infect, damage, or disrupt a computer system.
It spreads from one computer to another without the user’s knowledge.
👉 In simple words:
A computer virus is a harmful program that enters a computer and damages files or slows down the system.
Definition (Exam-Ready)
A computer virus is a malicious program that replicates itself and spreads to other computers, causing damage to data and system performance.
Characteristics of a Computer Virus
- It attaches itself to files or programs
- It spreads from one system to another
- It can replicate itself
- It may damage files or delete data
- It slows down the computer
How Computer Viruses Work
- The virus enters the computer.
- It attaches itself to a file or program.
- When the file is opened, the virus activates.
- It replicates and spreads to other files.
- It may corrupt or delete important data.
Types of Computer Viruses
1. Boot Sector Virus
- Attacks the boot sector of the hard disk.
- Activates when the computer starts.
2. File Virus
- Infects executable files (.exe, .com).
3. Macro Virus
- Infects documents like MS Word or Excel files.
4. Worm
- Spreads automatically through networks.
- Does not need user action.
5. Trojan Horse
- Appears as useful software.
- Steals information secretly.
Symptoms of Virus Infection
- Computer becomes slow
- Frequent crashes
- Files get deleted automatically
- Strange pop-up messages
- Programs stop working properly
Causes of Virus Spread in Computer
Viruses spread due to unsafe practices. Below are the main causes:
1. Using Infected USB Drives
- Inserting unknown or infected pen drives.
- Virus transfers automatically.
Example:
Using a friend’s infected USB in your computer.
2. Downloading Software from Untrusted Websites
- Free cracked software may contain viruses.
Example:
Downloading games from illegal websites.
3. Opening Suspicious Email Attachments
- Email attachments may contain harmful files.
Example:
Opening an unknown “lottery winner” attachment.
4. Visiting Unsafe Websites
- Some websites automatically download malware.
5. Lack of Antivirus Software
- No protection increases risk.
6. Not Updating Operating System
- Old systems have security weaknesses.
7. File Sharing in Network
- Infected files can spread in LAN.
Effects of Computer Virus
- Data loss
- System slowdown
- File corruption
- Theft of personal information
- Financial loss
Prevention of Computer Viruses
1. Install Antivirus Software
Use trusted antivirus programs like:
- Quick Heal
- Norton Antivirus
- McAfee
2. Do Not Open Unknown Emails
3. Avoid Pirated Software
4. Scan USB Drives Before Use
5. Keep System Updated
6. Use Firewall Protection
Difference Between Virus, Worm and Trojan
| Feature | Virus | Worm | Trojan |
|---|---|---|---|
| Needs Host File | Yes | No | No |
| Self-Replicating | Yes | Yes | No |
| Spreads Automatically | Sometimes | Yes | No |
| Disguised as Useful Program | No | No | Yes |
Real-Life Example
Imagine a virus like a biological virus:
- It enters the body (computer),
- Multiplies,
- Spreads to others,
- Causes damage.
Relational Operators Explained with Examples
