CBSE Class 7 Computer
📘 Chapter – 11: Viruses and Antiviruses
💻 What is a Computer Virus?
➥ A computer virus is a harmful program designed to enter a computer without permission and damage data, software, or system performance.
➭ It can replicate itself and spread from one device to another.
➭ It attaches itself to program files, boot sector, macros, emails, etc.
➭ It spreads through pen drives, downloads, email attachments, and pirated software.
🎯 Computer Viruses are Designed To (Purpose of Viruses):
➭ Corrupt or delete files.
➭ Steal personal or confidential data.
➭ Slow down the computer.
➭ Damage the operating system.
➭ Disable antivirus or security tools.
➭ Display unwanted pop-ups.
🌍 Origin of Computer Viruses
➭ First virus created was Creeper Virus (1971).
➭ Fred Cohen first used the term "Computer Virus" in 1983.
➭ Early viruses were made for fun or experiments, but modern viruses are created for money, data theft, hacking, and cybercrime.
- ➭ First PC virus: Brain Virus (1986)
- ➭ Created by hackers, students, cybercriminals, malicious programmers
🗂️ Types of Files Viruses Infect (Infection Targets)
1️⃣ Program (File) Viruses
✔ Infect executable files like .exe, .com, .bat, .bin, .ovl, .drv, .sys.
✔ Spread when the infected file is run.
Examples: Cascade, Sunday, Vienna, Crazy.A., Acid Rain
2️⃣ Macro Viruses
✔ Infect Microsoft Office documents.
✔ Written in VBA (Visual Basic for Applications).
Examples: Melissa, WM Concept, Nimda.
3️⃣ Boot Sector Viruses
✔ Infect the boot sector or Master Boot Record (MBR).
✔ Prevent system from booting properly.
Examples: Michelangelo, Brain, Stoned, Polyboot.B, Danish Boot, Devil.941, Parity Boot.
🦠 Malware
➭ Malware means Malicious Software designed to harm a computer.
➭ It includes viruses, worms, trojans, spyware, ransomware etc.
➭ Malware can damage files, steal data, slow down the system, or control the device.
➭ It spreads through internet downloads, email attachments, USB drives, and fake apps.
🐛 Worms
➭ Worms are malware that can replicate themselves without user action.
➭ They spread through emails, networks, and the internet.
➭ Worms make many copies and slow down computers and networks.
➭ They do not need a host file like viruses.
➭ Examples: ILOVEYOU, Nimda, SQL Slammer.
🐴 Trojan Horses
➭ A Trojan Horse looks like a safe program but contains hidden harmful code.
➭ Trojans do not replicate like viruses or worms.
➭ They can give hackers remote access to your computer.
➭ Trojans can steal data, delete files, and install more malware.
➭ Examples: Zeus Trojan, Beast Trojan, Back Orifice.
👁️ Spyware
➭ Spyware secretly monitors user activity.
➭ It records keystrokes, browsing history, passwords, and private information.
➭ Spyware sends collected data to hackers without your knowledge.
➭ It slows down the device and causes unwanted ads.
➭ Examples: CoolWebSearch, DarkHotel Spyware.
🛡️ Computer Viruses and Malwares
| Virus Type | Example | Infection Target | Harmful Effect | Technique Used |
|---|---|---|---|---|
| Program/File Virus | Jerusalem, Cascade | .exe, .com files | Corrupts/executes attack when program runs | Modifies program files |
| Macro Virus | Melissa, Concept | MS Office documents (.doc, .xls) | Corrupts or deletes content in documents | Embedded in macros |
| Boot Sector Virus | Disk Killer, Stoned | Boot sector/MBR of drives | Prevents system boot, data inaccessible | Infects at startup |
| Worm | Conficker, ILOVEYOU | Entire network via vulnerabilities | Spreads rapidly, slows network, data loss | Self-replicates via network |
| Trojan Horse | Zeus, Tinba | Installs as legitimate software | Steals data, opens backdoors | Disguised as safe software |
| Spyware | CoolWebSearch | All files or browser | Steals info, browser hijacking | Monitors user activity |
| Ransomware | CryptoLocker | All files | Encrypts data, demands ransom | Encrypts user files |
🛑 Symptoms of Virus Attack
1. Computer becomes slow and takes longer to open programs or files.
2. Files may disappear, get renamed, or become inaccessible.
3. Frequent pop-up messages appear unexpectedly.
4. System may restart automatically without warning.
5. Antivirus or security software may get disabled.
6. Unknown icons or programs appear on the desktop.
7. Programs may fail to open or respond.
8. High internet or data usage may occur due to malware.
9. System crashes or freezes frequently.
💥 Harmful Effects of Viruses
1. Loss of important data and files from your system.
2. Operating system damage, making the computer unstable.
3. Privacy loss due to spyware or keyloggers stealing information.
4. Identity theft or misuse of personal information.
5. Financial loss if sensitive data like banking info is stolen.
6. Network infection spreading viruses to other devices.
7. Overall slow performance and frequent errors.
🛡️ Preventing Virus Infections
1. Install a trusted antivirus software and keep it updated.
2. Scan your computer regularly for viruses and malware.
3. Avoid opening unknown email attachments or links.
4. Do not download or use pirated software or apps.
5. Keep your operating system and software updated with the latest patches.
6. Scan USB drives and external devices before using them.
7. Enable firewall protection to block unauthorized access.
8. Take regular backups of important files.
🧰 Antivirus Software
➥ Antivirus is a software program designed to detect, prevent, and remove malicious programs, known as viruses, from a computer or device.
➯It provides real-time protection, scans files, emails, and downloads, and prevents unauthorized access or damage caused by malware.
1. Antivirus software detects, removes, and protects against viruses.
2. Provides real-time protection against malware threats.
3. Scans emails, downloads, and files for malicious content.
4. Popular antivirus software include:
- McAfee
🔵 Quick Heal Total Security – Features
1. Provides real-time virus and malware protection.
2. Includes anti-spyware, anti-malware, and firewall features.
3. Scans USB drives, emails, and downloaded files.
4. Safe banking and online transaction security.
5. Parental control to monitor children’s activities.
6. Ransomware protection to prevent data encryption attacks.
🔍 Scanning and Removing Viruses
1. Open your antivirus software and select the type of scan:
- Quick Scan: Checks critical system areas for viruses.
- Full System Scan: Scans all files, drives, and folders.
- Custom Scan: Scan specific folders or files.
- Memory Scan: Checks RAM for active malware.
- Boot Time Scan: Scans before the operating system loads.
- Vulnerability Scan: Checks system for security weaknesses.
2. Antivirus detects infected files by comparing with virus signatures.
3. Detected files are cleaned, quarantined (isolated), or deleted.
4. After cleaning, restart the system to complete the process.
5. Repair any damaged files if the antivirus provides a repair option.
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