Virus, Worm, Trojan, Spyware, Adware

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1️⃣ COMPUTER VIRUS

Definition

A Computer Virus is a malicious software program that attaches itself to a legitimate file or program and spreads from one computer to another, causing damage to data and system performance.

Meaning of VIRUS

VIRUS = Vital Information Resources Under Siege

Characteristics

  • Requires a host file to activate

  • Self-replicating

  • Spreads through user action

  • Can corrupt or delete files

  • Slows down system performance

How Virus Spreads

  • Infected USB drives

  • Email attachments

  • Pirated software

  • Infected websites

  • Network file sharing

Types of Computer Virus

  1. Boot Sector Virus – Infects the boot sector of hard disk.

  2. File Infector Virus – Attaches to executable files (.exe).

  3. Macro Virus – Infects MS Word/Excel documents.

  4. Polymorphic Virus – Changes its code to avoid detection.

  5. Multipartite Virus – Infects both boot sector and files.

Symptoms

  • System becomes slow

  • Frequent crashes

  • Unknown files created

  • Programs fail to open

  • Automatic restart

Prevention

  • Install updated antivirus software

  • Avoid pirated software

  • Scan USB drives before use

  • Keep operating system updated

2️⃣ WORM

Definition

A Worm is a standalone malware program that spreads automatically across networks without attaching to any host file.

Characteristics

  • Self-replicating

  • Does not require user action

  • Spreads rapidly through networks

  • Consumes bandwidth

How Worm Spreads

  • Network vulnerabilities

  • Email spam

  • Internet connections

  • File sharing systems

Damage Caused

  • Network congestion

  • System slow down

  • Server crash

  • Data overload

Virus vs Worm (Important Difference)

VirusWorm
Needs host fileDoes not need host file
Requires user actionSpreads automatically
Slower spreadFaster spread

Prevention

  • Enable firewall

  • Update system regularly

  • Use network security tools

3️⃣ TROJAN HORSE

Definition

A Trojan Horse is a malicious program that appears as legitimate software but secretly performs harmful actions in the background.

Origin of Name

Named after the Greek story of the “Trojan Horse,” where enemies entered the city hidden inside a wooden horse.

Characteristics

  • Does not self-replicate

  • Creates backdoor access

  • Allows remote control by hackers

Types of Trojan

  1. Backdoor Trojan – Gives remote access to attacker

  2. Banking Trojan – Steals financial data

  3. Downloader Trojan – Downloads other malware

  4. Ransom Trojan – Locks system and demands ransom

Damage Caused

  • Password theft

  • Banking fraud

  • Data stealing

  • Spy activities

Prevention

  • Download software from trusted sources

  • Avoid cracked programs

  • Use updated antivirus

4️⃣ SPYWARE

Definition

Spyware is malicious software that secretly monitors user activities and collects sensitive information without permission.

What Spyware Collects

  • Keystrokes (Keylogger)

  • Passwords

  • Browsing history

  • Personal information

  • Banking details

Types of Spyware

  1. Keylogger – Records keyboard input

  2. Tracking Cookies – Tracks browsing habits

  3. System Monitor – Records all activities

Symptoms

  • Excessive pop-ups

  • Browser redirection

  • Slow performance

  • Unknown toolbars

Prevention

  • Install anti-spyware software

  • Use pop-up blocker

  • Avoid suspicious websites

5️⃣ ADWARE

Definition

Adware is software that automatically displays unwanted advertisements on your computer or browser.

Characteristics

  • Shows pop-up ads

  • Redirects browser

  • May collect user data

Difference Between Adware and Spyware

AdwareSpyware
Displays adsSteals data
Sometimes legalMostly illegal
Focus on advertisingFocus on spying

Symptoms

  • Too many advertisements

  • Homepage changes automatically

  • Browser opens unwanted tabs

Prevention

  • Install ad blocker

  • Remove unknown browser extensions

  • Use antivirus software

🔥 Comparison Table (Exam Important)

FeatureVirusWormTrojanSpywareAdware
Self-replicatingYesYesNoNoNo
Needs Host FileYesNoNoNoNo
Spreads AutomaticallyNoYesNoNoNo
Steals DataSometimesRareYesYesSometimes
Shows AdsNoNoNoNoYes

🛡 General Security Measures

  • Use strong passwords

  • Enable two-factor authentication

  • Backup important data regularly

  • Install antivirus and firewall

  • Avoid unknown downloads

  • Keep system updated

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