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Security Aspects – Class 12 Computer Science notes, important questions and MCQs

NCERT Class 12 Computer Science, chapter 12. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Network security protects computers, networks and data from threats such as malware, unauthorised access and attacks. Malware includes viruses, worms, trojans, ransomware, spyware and adware. Defences include antivirus software, firewalls, secure protocols such as HTTPS, careful handling of cookies, and safe practices. Hacking may be ethical or unethical, and common network attacks include denial of service, snooping and eavesdropping.

Threats and malware

A virus attaches itself to a program or file and spreads when the infected file is run; a worm spreads by itself across networks without needing a host file; a trojan appears to be useful software but carries hidden harmful code.
Ransomware encrypts or locks a victim's data and demands payment; spyware secretly collects user information; adware shows unwanted advertisements; keyloggers record keystrokes to steal passwords.
Malware spreads through infected downloads, email attachments, removable drives, malicious websites and networks.

Protection and attacks

Antivirus software detects malware using signature-based detection (matching known patterns), heuristic analysis and sandbox testing; it must be updated regularly.
A firewall monitors and filters incoming and outgoing network traffic according to rules; it can be hardware or software. HTTPS encrypts web traffic using SSL/TLS; cookies store small pieces of data from websites, and third-party cookies can be used for tracking.
Hackers may be white hat (ethical, testing security with permission), black hat (crackers, malicious) or grey hat; attacks include denial of service (DoS) and distributed DoS (flooding a server with requests), intrusion, snooping and eavesdropping (secretly intercepting communication). Safe practices include strong passwords, updates, backups, avoiding unknown links and using verified software.

Key terms

Malware: malicious software designed to harm or exploit systems
Worm: self-replicating malware that spreads across networks without a host
Trojan: malware disguised as useful software
Firewall: a system that filters network traffic according to security rules
Denial of service: an attack that floods a system so legitimate users cannot access it

Important questions with answers

Distinguish between a virus and a worm.2 marks

A virus attaches itself to a host program or file and spreads only when the infected file is executed or shared. A worm is a standalone program that replicates itself and spreads automatically across networks without needing a host file or user action, often consuming bandwidth.

What is a firewall and why is it used?3 marks

A firewall is a hardware device or software that monitors incoming and outgoing network traffic and allows or blocks it based on predefined security rules. It is used to prevent unauthorised access to a network or computer, block malicious traffic and protect against attacks from the internet.

Explain the different types of malware and the measures to protect against them.5 marks

Malware is malicious software designed to damage systems, steal data or gain unauthorised access. A virus attaches to files or programs and spreads when the infected file is run, corrupting or deleting data. A worm is self-replicating and spreads through networks without a host, slowing systems and networks. A trojan horse disguises itself as useful software, such as a free game, but performs harmful actions in the background, such as creating a backdoor for attackers. Ransomware encrypts the victim's files and demands payment for the decryption key. Spyware secretly monitors user activity and collects personal information such as passwords and browsing habits. Adware displays unwanted advertisements and may track users, and keyloggers record keystrokes to capture passwords. Protective measures include installing reputable antivirus software and keeping its definitions updated; using a firewall to filter network traffic; regularly updating the operating system and applications to fix security vulnerabilities; downloading software only from trusted sources; not opening suspicious email attachments or links; scanning pen drives before use; using strong passwords and two-factor authentication; visiting only secure HTTPS websites for sensitive transactions; managing cookies and privacy settings; and keeping regular offline backups, so that data can be restored after an attack such as ransomware.

Quick revision

Types of malware.
How malware spreads.
Antivirus, firewall, HTTPS, cookies.
Hackers and network attacks; safe practices.

Exam tips

Virus needs a host file; worm does not; trojan pretends to be useful.
Check for HTTPS and a padlock before entering sensitive data.

Practice MCQs

Malicious software is commonly called
1. freeware
2. shareware
3. firmware
4. malware
Show answer
Answer: (d) malware. Viruses and worms are examples.
A system that filters incoming and outgoing network traffic is a
1. modem
2. browser
3. router only
4. firewall
Show answer
Answer: (d) firewall. It can be hardware or software.
Malware that locks data and demands payment is
1. adware
2. worm
3. spyware
4. ransomware
Show answer
Answer: (d) ransomware. Keep backups.
Malware that spreads across networks on its own without a host file is a
1. virus
2. cookie
3. trojan
4. worm
Show answer
Answer: (d) worm. Worms are self-replicating.
Software that appears useful but contains hidden malicious code is a
1. worm
2. trojan horse
3. firewall
4. antivirus
Show answer
Answer: (b) trojan horse. It is named after the Greek story.
Ethical hackers who test security with permission are called
1. black hat hackers
2. white hat hackers
3. crackers
4. script kiddies
Show answer
Answer: (b) white hat hackers. They help fix weaknesses.
Flooding a server with huge numbers of requests from many computers so it cannot serve users is
1. snooping
2. phishing
3. distributed denial of service
4. eavesdropping
Show answer
Answer: (c) distributed denial of service. Many machines are used in DDoS.
Antivirus detection that matches files with patterns of known malware is
1. heuristic detection
2. firewall filtering
3. sandbox detection
4. signature-based detection
Show answer
Answer: (d) signature-based detection. It requires regular updates of definitions.

All chapters of Class 12 Computer Science

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.