Computer Security Fundamentals

Introduction to Computer Security

Definition: Computer security, also known as Cyber Security or IT Security, is a branch of Information Technology dedicated to protecting computers.
Purpose: Its primary goal is to protect computer systems, data, and information from unauthorized access, misuse, and malicious software (like viruses).

Methods to Provide Security

To secure computer systems and data, four main control methods are utilized:

Security Method	Description
1. System Access Control	Allows or restricts the use and modification of data. When a user logs in, the system determines what data is accessible based on their User ID.
2. Data Access Control	Monitors who can control specific data. It creates access rules based on the security levels of specific individuals, files, and objects.
3. System & Security Administration	Executes offline processes to either establish strict security protocols for a system or purposefully test/break its security.
4. System Design	Leverages and takes advantage of the foundational, built-in security features of both computer hardware and software.

Key Components of Computer Security

A robust computer security system relies on several core components:

Confidentiality: Ensuring that data and information are completely protected from being accessed by unauthorized or illegal individuals.
Non-Repudiation: Ensuring that the original sender of a message cannot deny having sent it.
Authentication: The process of verifying whether a user interacting with the system is valid (authorized) or invalid (unauthorized).
Access Control: Ensuring that users are only allowed to utilize the specific resources they have been granted permission to use.
Availability: Guaranteeing that system functions correctly and that valid users are never denied service or access.
Cryptography: The technical art of hiding or writing information secretly to keep data safe during transmission over the internet.
Stenography: The art of hiding a message along with its very existence, which helps maintain data confidentiality and integrity.
Integrity: Ensuring that information has not been altered by an unauthorized person in a way that a valid user cannot recognize.

Elements of Cryptography

Cryptography involves several technical steps to secure data:

Element	Description
Plain Text	The original, readable message provided as input.
Cypher	The process of transforming text bit-by-bit or character-by-character without changing its actual meaning.
Cipher Text	The coded or encrypted data that cannot be read directly by a user.
Encryption	The process of converting Plain Text into Cipher Text using a mathematical algorithm.
Decryption	The exact reverse of encryption; converting unreadable Cipher Text back into Plain Text.

Threats to Computer Security: Malware & Viruses

Malware (Malicious Software) represents programs strictly designed to harm computers, including Viruses, Worms, and Spyware.

Computer Virus:

A negative, destructive software program that takes control of a PC to perform abnormal actions.
Viruses automatically copy themselves into the system and attach to other programs to spread the infection.
They can damage the boot block, operating system, system area, files, and application programs.

Sources of Cyber Attacks

Viruses and malware usually enter a system through the following sources:

Downloadable Programs: Executable files (like games and screensavers) are major virus sources. Always scan programs before downloading from the internet.
Cracked Software: These heavily carry viruses and bugs that are extremely hard to remove. Only download information from trusted sources.
e-Mail Attachments: A primary carrier of viruses that can easily manipulate users.
The Internet: Careless clicking and downloading by unaware users is highly responsible for spreading viruses.
Unknown CDs: Leaving a CD in the drive while the computer is inactive can cause auto-booting, increasing the chance of a virus attack.

Classification of Computer Viruses

Understanding different virus types is highly important for exam preparation:

Virus Type	Behavior & Characteristics	Example(s)
Direct Action Virus	Activates itself immediately when its host file is used. It only infects files mentioned in the `autoexec.bat` folder path.	Vienna Virus
Overwrite Virus	Highly destructive; completely deletes the data and information stored within the files it infects.	Way, Trivial.88-D
Boot Sector Virus	Also known as Master Boot Record virus. Resides in the boot sector of a hard disk/floppy disk and spreads the moment the computer boots up.	Anti exe
Macro Virus	Only infects applications and programs that contain macros, such as `.doc`, `.xls`, and `.pps` files.	Melissa.A
File System Virus	Also called a Cluster/Directory virus. It alters the directory path of files, causing severe memory management issues.	Dir-2 Virus
Polymorphic Virus	Encodes or encrypts itself differently every single time it infects a system, creating countless variations to avoid detection.	ElKern, Tuareg

1. Additional Types of Computer Viruses

Continuing from the previous classification, here are more virus types you need to know:

FAT Virus (File Allocation Table): Stores information regarding the exact location of files and the unused memory space in the system (e.g., Link Virus).
Web Scripting Virus: Infects the complex codes used on websites to display interesting content (e.g., J.S. Fortnight).
Multipartite Virus: Spreads through multiple methods, such as during Operating System installation (e.g., Flip).
Resident Virus: Hides and settles completely within the system's RAM. It becomes active the moment the OS runs, infecting every opened file. It remains active even after the malicious code executes (e.g., Randex, Meve).

Important Timeline of Major Computer Viruses

Year	Name of Virus	Year	Name of Virus
1971	Creeper	2003	Blaster
1982	Elk Cloner	2004	Sasser
1988	The Morris Internet Worm	2010	Stuxnet
1999	Melissa	2011	Trojan
2000	I Love You	2012	Rootkit
2001	Code Red	2014	Generic PUP
2003	SQL Slammer	2014	Net Worm

2. Other Major Types of Malware

"Malware" is an umbrella term. Apart from viruses, you must know these key threats:

Worms: A standalone malware program that automatically copies itself to spread to other computers. They hide as invisible files, making them hard to detect, and severely damage network bandwidth (e.g., Bagle, I love you, Morris, Nimda).
Trojans (Trojan Horse): A non-self-replicating malware. It disguises itself as a useful or desirable program but secretly grants unauthorized access to the user's PC. It spreads mostly via internet-driven applications (e.g., Beast, Sub 7, Zeus, Zero Access Rootkit).
Spyware: Secretly installs on a PC to constantly monitor user activities and collect personal data. This data is often transmitted over the internet to a third party (e.g., Cool Web Search, Keyloggers, Zlob Trojan).
Adware: A software package designed to forcefully and automatically display unwanted advertisements on your screen.
Rootkits: Dangerous malware that grants a hacker administrative-level control over a system without anyone noticing. It is extremely difficult to remove, sometimes requiring a full OS reinstallation.

3. Recognizing a Malware Attack

Effects of a Virus on a PC

Monitors user activity and changes PC settings.
Reduces system efficiency and increases boot time.
Destroys data present on local disks.
Manipulates memory size (increases or decreases inexplicably).
Displays error messages and arrays of unwanted ads.
Negatively impacts network and internet connections.

Symptoms of an Attack

System runs remarkably slow or crashes/restarts repeatedly.
Mismatched or odd messages appear on the screen.
Important files go missing.
Drive becomes completely inaccessible.
Antivirus software fails to run or install.
The mouse pointer graphic changes automatically.

4. Advanced Security Threats

Hackers use various techniques to steal data. Key definitions for exams:

Threat Term	Definition / Behavior
Spoofing	Accessing unauthorized data without the authorized user's knowledge. (e.g., IP Spoofing is used to illegally access network resources).
Salami Technique	Stealing funds by secretly separating tiny, unnoticeable amounts of money from large transactions handled by a system.
Hacking	The process of intruding into network-connected computers. This can lead to a DOS (Denial-of-Service) attack, blocking valid users from resources.
Cracking	The act of breaking software or passwords. It utilizes password crackers, trojans, and war dialers.
Phishing	An internet fraud attempting to steal sensitive credentials (passwords, credit card details) by tricking or misleading the user.
Spam	The heavy misuse of messaging systems to send massive amounts of unwanted emails.

5. Solutions & Security Mechanisms

To defend against the threats mentioned above, the following tools are used:

Antivirus Software: Programs explicitly designed to find, block, and destroy viruses, spyware, worms, and trojans (e.g., Avast, AVG, Kaspersky, Norton, McAfee).
Firewall: Can be hardware or software. Its primary job is to control incoming and outgoing network traffic by strictly analyzing data packets.
Digital Signature: An electronic signature used to authenticate sent messages and guarantee that a document is original.
Digital Certificate: An electronic copy used in messages to prove security credentials (shows exactly who sent it and to whom).
Proxy Server (Application-Level Gateway): Acts as a middleman between the user and the server. It hides the real network address and intercepts messages for security.
Application Gateway: Applies strict security rules for specific applications, like FTP (File Transfer Protocol) and Telnet.
Patches: A small piece of software specifically created to fix bugs or improve an existing program.

6. Passwords and File Access Permissions

Password: A secret string of characters used to authenticate user identity.
- Weak Passwords: Easy to guess (Name, DOB).
- Strong Passwords: Hard to crack, combining alphabets, numbers, and symbols.

3 Types of File Permissions:

Read Permission: User can only view the contents.
Write Permission: User can modify, edit, or delete file contents.
Execute Permission: User is strictly allowed to run/execute the file.

7. Must-Know Exam Facts (Direct One-Liners)

VIRUS Full Form: Vital Information Resource Under Siege.
First PC Boot Sector Virus: Brain (Identified in 1986).
First Self-Replicating Virus: Creeper, written by Bob Thomas in 1971 at BBN Technologies.
First Virus "In the Wild": Elk Cloner.
First Virus seen in India: Happy Birthday Joshi.
Gamima Virus: Specifically spreads through removable flash drives.
TLS (Transport Layer Security): A cryptographic protocol providing secure HTTP connections to ensure data privacy and integrity between two parties.
Payload: The specific malicious code inside a worm designed for massive propagation.
Logic Bomb vs Time Bomb: A Logic Bomb triggers under specific favorable conditions but doesn't self-replicate. A Time Bomb activates at a predetermined time.
Masquerading: An attacker pretending to be a legitimate user to gain privileges.
Eavesdropping: Secretly monitoring the contents of a transmitted message.

Common Internet Slang (Behavioral Threats)

Cyber Bully: A person who harasses, defames, or spams others online.
Troll: Defames others on forums/chats by mimicking or mocking them.
Griefer: A player in an online game whose sole purpose is to harass other players.
Flamer: Someone who posts low-level, highly insulting comments on message boards.
Egosurfer: A person who searches the internet for their own name or info about themselves.
Noob: A new, untrained person who is ignorant of website rules.

Summary / Quick Revision Notes 🚀

Cyber Security Purpose: Protection of computer systems, hardware, and data from illegal access and viruses.
4 Access Controls: System Access, Data Access, System/Security Admin, and System Design.
Core Security Goals:
- Confidentiality (no illegal access).
- Integrity (no unauthorized changes).
- Availability (valid users get access).
- Non-Repudiation (sender can't deny sending).
Cryptography Lifecycle: Plain Text ➔ Encryption ➔ Cipher Text ➔ Decryption ➔ Plain Text.
Malware: Stands for "Malicious Software". Includes viruses, worms, and spyware.
Major Attack Sources: Downloadable files, cracked software, email attachments, careless internet browsing, and booting from unknown CDs.
Virus Key Traits:
- Boot Sector: Attacks on computer startup.
- Overwrite: Deletes file contents entirely.
- Macro: Attacks document files (.doc, .xls).
- Polymorphic: Changes its code continuously to hide.

Viruses attach to files. Resident hides in RAM, Multipartite uses multiple attack vectors, Web Scripting attacks site codes.
Worms vs Trojans: Worms replicate automatically and destroy bandwidth; Trojans disguise themselves as helpful apps to steal access but do not self-replicate.
Key Attack Vectors: Spoofing (secretly accessing data), Phishing (stealing passwords via fake pages), Hacking (network intrusion leading to DOS), Salami (stealing tiny fractions of money).
Defense Mechanism: Antivirus removes threats, Firewalls block bad data packets, Digital Signatures/Certificates prove identity and originality.
File Permissions: Remember RWX -> Read (View), Write (Edit), eXecute (Run).
Historical Firsts: First Virus = Creeper (1971). First PC Boot Virus = Brain (1986). First in India = Happy Birthday Joshi.
VIRUS = Vital Information Resource Under Siege.

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