Saturday, June 13, 2026

Unit 5 — Malware, OS Hardening, Firewall, Digital Signature Standard

 

From MCA553 (Principles of Cryptography and Cyber Security). 



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Malware


Malware = Malicious Software


Software designed to damage, steal, spy on, or disrupt computer systems.


Objectives:


Steal information


Destroy data


Spy on users


Gain unauthorized access




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Types of Malware


1. Virus


A virus attaches itself to a file or program and spreads when that file runs.


Characteristics:


Requires user action


Can corrupt files


Slows system performance



Example: Infected USB drive.



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2. Worm


A worm spreads automatically through networks.


Characteristics:


No user action required


Self-replicating


Consumes bandwidth



Example: WannaCry Worm.



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Difference Between Virus and Worm


Virus Worm


Needs host file Independent

User action needed Automatic spread

Slower spread Faster spread




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3. Trojan Horse


Malware disguised as legitimate software.


Example: Fake antivirus software.


Characteristics:


Looks genuine


Creates backdoor access


Steals information




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4. Rootkit


Designed to hide malware activities.


Functions:


Hides files


Hides processes


Hides network connections



Danger: Very difficult to detect.



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5. Bot (Robot)


An infected computer controlled remotely by attackers.


A collection of bots forms a:


Botnet


Used for:


Spam attacks


DDoS attacks


Cryptocurrency mining




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6. Adware


Displays unwanted advertisements.


Effects:


Pop-up ads


Browser redirection


Slow performance




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7. Spyware


Secretly collects information.


Steals:


Passwords


Banking details


Browsing history




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8. Ransomware


Encrypts files and demands money.


Process:


Files Locked

      ↓

Payment Demanded

      ↓

Decryption Key Promised


Example: WannaCry Ransomware.



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9. Zombie


A compromised computer controlled remotely.


Used in:


DDoS attacks


Botnets



User usually does not know their system is infected.



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Malware Analysis


Process of studying malware.


Purpose:


Understand behavior


Identify threats


Develop defenses



Types:


Static Analysis


Without running malware.


Examines:


Code


Strings


File structure




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Dynamic Analysis


Running malware in a controlled environment.


Observes:


Network activity


File modifications


Registry changes




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OS Hardening


OS Hardening means securing an operating system by reducing vulnerabilities.


Purpose:


Increase security


Reduce attack surface




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Process Management


Monitor running processes.


Actions:


Stop suspicious programs


Limit privileges




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Memory Management


Protect memory from unauthorized access.


Methods:


Access control


Memory protection




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Task Management


Control applications and services.


Benefits:


Remove unnecessary programs


Improve security




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Windows Registry Security


Registry stores system settings.


Hardening Steps:


Restrict access


Backup registry


Remove malicious entries




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Services Configuration


Disable unnecessary services.


Examples:


Unused FTP services


Unused Remote Access services



Benefits:


Reduced attack surface




---


Antivirus Protection


Antivirus software detects and removes malware.


Functions:


Scan files


Real-time protection


Quarantine threats



Examples:


Microsoft Defender


Quick Heal


Avast




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Anti-Spyware Tools


Designed specifically to detect spyware.


Functions:


Remove tracking software


Protect privacy




---


System Tuning Tools


Improve performance and security.


Functions:


Remove junk files


Optimize startup


Clean registry




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Anti-Phishing Tools


Protect users from fake websites and emails.


Features:


URL checking


Email scanning


Browser protection




---


Firewall


A firewall monitors and controls network traffic.


Acts as a security gate between:


Internet

   ↓

Firewall

   ↓

Private Network



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Firewall Design Principles


1. All traffic must pass through firewall


No direct access.



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2. Only authorized traffic allowed


Rules determine access.



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3. Firewall itself must be secure


Cannot be easily attacked.



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Types of Firewalls


Packet Filtering Firewall


Checks packets individually.



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Stateful Inspection Firewall


Tracks active connections.



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Application Firewall


Protects applications.


Example: Web Application Firewall (WAF)



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Trusted Systems


Systems designed with built-in security mechanisms.


Features:


Access control


Auditing


Authentication




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Digital Signature


Digital signature proves:


1. Sender identity



2. Data integrity



3. Non-repudiation




Uses:


Private Key


Public Key




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Authentication Protocol


Rules used to verify identity.


Examples:


Password Authentication


OTP Authentication


Kerberos


Multi-Factor Authentication (MFA)




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Digital Signature Standard (DSS)


A standard developed by the U.S. government for digital signatures.


Purpose:


Secure electronic communication


Verify authenticity



Benefits:


Authentication


Integrity


Non-repudiation




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Important Exam Questions


Short Questions


1. What is Malware?



2. Define Virus.



3. Define Worm.



4. What is Trojan Horse?



5. What is Ransomware?



6. What is OS Hardening?



7. What is a Firewall?



8. What is DSS?





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Long Questions


1. Explain various types of malware.



2. Differentiate Virus and Worm.



3. Explain OS Hardening techniques.



4. Discuss Firewall design principles.



5. Explain Digital Signature Standard.



6. Explain Malware Analysis techniques.





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One-Day Exam Revision (MCA553)


Remember:


CIA = Confidentiality, Integrity, Availability


Cyber Forensics = Investigation of digital crimes


RSA = Public Key Cryptography


Diffie-Hellman = Key Exchange


AES = Modern Encryption Standard


Triple DES = DES × 3


Hash Function = Fixed-size fingerprint


MAC = Message Authentication Code


Virus = Needs host file


Worm = Self-spreading


Trojan = Fake software


Ransomware = Encrypts files for money


Firewall = Controls network traffic


DSS = Digital Signature Standard



You have now completed Cyber Security (MCA553) from your Semester III syllabus. Next, I recommend Machine Learning Techniques (MCA556) because it is one of the easiest and most scoring papers in Semester III. 

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