Computer Virus

Q: What Is a Computer Virus?

See the detailed explanation in this article about computer virus.

A Computer Virus is a malicious software program that attaches itself to other programs or files and spreads from one computer to another, causing harm by corrupting data, stealing information, or disrupting normal computer operations. Like a biological virus, it needs a host to survive and can replicate itself.

Quick Summary

Computer viruses are harmful programs that damage or disrupt computer systems
They spread by attaching to files, emails, or removable drives
Viruses can delete files, steal data, slow down systems, or crash computers
Antivirus software helps prevent and remove virus infections
Safe computing habits reduce the risk of virus attacks

What Is a Computer Virus?

A computer virus is a type of malicious software (malware) created to cause damage to computer systems. The name “virus” comes from biological viruses because computer viruses behave similarly. They attach themselves to healthy programs, multiply, and spread to other computers.

When you run an infected program, the virus activates and starts its harmful activities. It might copy itself to other files on your computer or send itself to your contacts through email. Some viruses work immediately, while others hide and activate on a specific date or after certain actions.

How Computer Viruses Work

Computer viruses follow a typical pattern:

Infection: The virus enters your computer through a downloaded file, email attachment, infected USB drive, or compromised website.
Activation: When you open the infected file, the virus code runs and takes control.
Replication: The virus copies itself to other programs and files on your computer.
Spread: It tries to move to other computers through networks, email, or shared drives.
Payload Delivery: The virus executes its harmful actions, which could be immediate or delayed.

Types of Computer Viruses

Virus Type	How It Works	Example Effect
Boot Sector Virus	Infects the boot sector of hard drives or USB drives	Computer fails to start properly
File Infector Virus	Attaches to executable files (.exe, .com)	Programs crash or behave strangely
Macro Virus	Hides in documents (Word, Excel) that use macros	Documents get corrupted or send themselves to contacts
Polymorphic Virus	Changes its code each time it spreads	Hard for antivirus to detect
Resident Virus	Stays in computer memory (RAM)	Infects files continuously while computer runs
Multipartite Virus	Attacks both boot sector and files	Very difficult to remove completely
Web Scripting Virus	Uses browser security holes	Pop-ups, redirects, data theft

Effects of Computer Viruses

On Individual Users

Data loss: Viruses can delete important files, school projects, or family photos permanently
Slow performance: Infected computers run very slowly because the virus uses system resources
System crashes: The computer freezes, restarts unexpectedly, or won’t turn on
Privacy breach: Some viruses steal passwords, bank details, or personal information
Financial loss: Costs money to repair or replace damaged computers
Identity theft: Criminals use stolen data to impersonate victims

On Organizations and Businesses

Business disruption: Banks, hospitals, schools cannot operate normally
Financial damage: Companies lose money from downtime and repairs
Data breach: Customer information gets exposed or stolen
Reputation damage: Customers lose trust in affected companies
Legal problems: Organizations face lawsuits if customer data is compromised

Real Nigerian example: In 2020, several Nigerian banks faced service disruptions due to malware attacks, preventing customers from accessing their accounts through mobile apps and ATMs.

How Viruses Spread

Spread Method	Description	Prevention
Email Attachments	Virus hides in files sent via email	Don’t open attachments from unknown senders
Infected Websites	Visiting compromised sites downloads virus	Avoid suspicious websites, use browser protection
USB Drives	Virus copies itself to flash drives	Scan all USB drives before opening files
Software Downloads	Free software from untrusted sources contains viruses	Download only from official websites
Network Sharing	Spreads through shared folders on networks	Use firewalls and secure network settings
Social Media	Malicious links shared on Facebook, WhatsApp	Don’t click suspicious links, even from friends
Pirated Software	Cracked programs often contain viruses	Use genuine, licensed software

Signs Your Computer Has a Virus

Computer runs much slower than normal
Programs crash or freeze frequently
Unknown programs appear in your startup menu
Files disappear or become corrupted
Hard drive space decreases for no reason
Strange messages or pop-ups appear constantly
Emails are sent from your account without your knowledge
Antivirus software stops working or can’t update
Browser homepage changes without permission
Excessive hard drive activity even when idle

Preventing Computer Viruses

Essential Protection Measures

Install Antivirus Software: Use reliable programs like Avast, AVG, Norton, or Kaspersky. Keep them updated daily.
Update Your System: Install Windows/Mac updates promptly. They fix security holes viruses exploit.
Use a Firewall: Enable built-in firewall to block unauthorized network access.
Be Careful with Email: Don’t open attachments from strangers. Verify sender identity before clicking links.
Download Wisely: Only download software from official websites. Avoid pirated programs.
Scan USB Drives: Always scan external drives before opening any files.
Backup Regularly: Keep copies of important files on external drives or cloud storage.
Use Strong Passwords: Create complex passwords and change them regularly.
Avoid Public WiFi: Don’t access banking or sensitive information on public networks without VPN.
Educate Yourself: Learn to recognize phishing emails and suspicious websites.

Removing Computer Viruses

If your computer is infected:

Disconnect from Internet: Stop the virus from spreading or receiving commands
Boot in Safe Mode: Restart computer in Safe Mode (F8 during startup on Windows)
Run Antivirus Scan: Perform full system scan with updated antivirus
Delete Infected Files: Quarantine or delete files identified as threats
Clean Temporary Files: Clear browser cache and temp folders
Update Everything: Install all pending system and software updates
Change Passwords: Update all passwords after cleaning
Monitor System: Watch for unusual behavior in following days

If the virus persists, seek help from a computer professional or consider reinstalling the operating system.

Famous Virus Attacks in History

ILOVEYOU (2000): Email virus that affected 50 million computers worldwide, causing $10 billion in damages
WannaCry (2017): Ransomware that locked files and demanded payment, affected 200,000+ computers in 150 countries including Nigerian organizations
Melissa (1999): Spread through Word documents, crashed email systems globally
Conficker (2008): Infected millions of Windows computers, created massive botnet

Difference Between Viruses and Other Malware

Type	Characteristics	Main Threat
Virus	Needs host file, replicates when executed	File corruption, system damage
Worm	Self-replicating, doesn’t need host file	Network congestion, rapid spreading
Trojan	Disguises as legitimate software	Backdoor access, data theft
Ransomware	Encrypts files, demands payment	Data loss, financial extortion
Spyware	Secretly monitors user activity	Privacy invasion, identity theft
Adware	Displays unwanted advertisements	Annoyance, system slowdown

Common Exam Mistakes

Confusing virus with worm: Students say viruses self-replicate without a host. Remember: viruses NEED a host file, worms don’t.
Stating only negative effects: Examiners want specific examples like “deletes files,” “steals passwords,” not just “causes harm.”
Poor virus prevention explanation: Writing “use antivirus” without mentioning updates, scanning, or safe browsing habits.
Not distinguishing malware types: Calling all malware “viruses” when the question specifically asks about trojans or ransomware.
Vague spread methods: Writing “through internet” instead of specific methods like “email attachments” or “infected downloads.”

Practice Questions

Multiple Choice Questions

1. Which of these is the PRIMARY characteristic of a computer virus?
a) It spreads through networks only
b) It requires a host program to function ✓
c) It cannot be detected by antivirus
d) It only affects boot sectors

2. What type of virus infects Microsoft Word and Excel documents?
a) Boot sector virus
b) File infector virus
c) Macro virus ✓
d) Web scripting virus

3. Which of the following is NOT a common way viruses spread?
a) Email attachments
b) Infected USB drives
c) Properly licensed software from official sources ✓
d) Malicious website downloads

4. What should you do FIRST if you suspect your computer has a virus?
a) Delete all files
b) Disconnect from the internet ✓
c) Continue working normally
d) Send emails to warn friends

5. Which is an example of a sign that your computer might be infected?
a) Fast internet connection
b) Files saving properly
c) Programs running smoothly
d) Computer running very slowly ✓

6. What is the main difference between a virus and a worm?
a) Worms are less dangerous
b) Worms can replicate without a host file ✓
c) Viruses spread faster
d) Worms only affect networks

Theory Questions

1. Define computer virus and state four effects it can have on a computer system. (6 marks)

Answer guidance: Definition (2 marks), Four effects like deletes files, slows performance, steals data, crashes system (4 marks, 1 each)

2. Explain five ways computer viruses can spread from one computer to another. (10 marks)

Answer guidance: Email attachments, infected websites, USB drives, software downloads, network sharing – explain each method (2 marks each)

3. State six precautions computer users can take to prevent virus infection. (6 marks)

Answer guidance: Install antivirus, update system, scan USB drives, avoid suspicious emails, backup data, use firewall (1 mark each)

4. Distinguish between computer virus and computer worm. (4 marks)

Answer guidance: Virus needs host file and user action to spread; worm self-replicates without host file and spreads automatically (2 marks each for clear distinction)

5. A student’s computer suddenly became very slow and unknown programs started appearing. Describe the steps the student should take to remove the suspected virus. (8 marks)

Answer guidance: Disconnect internet, boot Safe Mode, run antivirus scan, delete infected files, clear temp files, update system, change passwords, monitor system (1 mark each)

Memory Aids

SPREAD – How viruses move:
Software downloads
Pirated programs
Removable drives (USB)
Email attachments
Attacked websites
Downloaded files

SCAN – Virus prevention basics:
Software (use antivirus)
Caution (be careful online)
Always update
Never trust unknown sources