Threats and Attacks (Virus, Worms, Trojan, DoS)

I/O Management and Security

I/O Software Layers (User Level, Device Drivers, Kernel)

Types ofAccess Control

Threats and  Attacks (Virus, Worms, Trojan, DoS)

Case Study: Modern Operating Systems

In the context of an Operating System (OS), threats and attacks target system resources like memory, files, CPU, and network services. The OS must defend against these to ensure confidentiality, integrity, and availability.

In computer security, a threat is any potential danger, while an attack is an actual attempt to harm or exploit a system. Below are some common types:

1. Virus

A virus is a malicious program that infects executable files or system areas and spreads when those programs run.

A virus is a malicious program that attaches itself to a file or program and spreads when that program is executed.

OS Perspective: (a point of view:)

Attaches to system files, boot sectors, or applications

Executes when the OS loads the infected program

Can modify or corrupt OS files

Impact on OS:

File system corruption

Slower system performance

System crashes or abnormal behavior

Characteristics:

Needs user action to spread (e.g., opening a file)

Infects files and programs

Can corrupt or delete data

📌 Example:

Opening an infected USB file that spreads the virus to your system.

2. Worm (in OS)

A worm is a standalone malware that spreads automatically over networks without user intervention.

A worm is a self-contained program that spreads across systems using OS/network vulnerabilities.

A computer worm is a type of malicious software (malware) that can self-                                                             replicate and spread across systems without requiring human intervention.

OS Perspective:

Exploits OS security flaws (e.g., open ports, weak services)

Does not require user action

Uses network stack managed by the OS

Impact on OS:

Heavy CPU and memory usage

Network congestion

System slowdown or freeze

Characteristics:

Self-replicating

Spreads rapidly across systems

Consumes network bandwidth

Example:

A worm spreading through a network and slowing down internet speed.

 

 

 

3. Trojan (Trojan Horse)

A Trojan is malicious software that disguises itself as legitimate software.

Once executed, it can perform various harmful actions, such as stealing sensitive information, granting remote access, or causing data loss. Trojans are often spread through social engineering tactics, such as phishing emails or disguised software downloads. They do not replicate themselves like viruses or worms but require user interaction to execute.

OS Perspective:

Installed as a normal application

Gains access using user privileges

May create a backdoor into the OS

Impact on OS:

Unauthorized access to files

Data theft

Remote control of the system

Characteristics:

Does not replicate itself

Tricks users into installing it

Creates backdoors for attackers

Example:

A fake app that looks useful but secretly steals your data.

4. DoS (Denial of Service) Attack

A DoS attack aims to make a system or network unavailable by overwhelming it with traffic.

A DoS attack targets the OS by overloading its resources, making services unavailable.

OS Perspective:

Exploits OS resource management (CPU, memory, sockets)

Floods system calls or network requests

May target kernel or server processes

Impact on OS:

Resource exhaustion (CPU, RAM, bandwidth)

System becomes unresponsive

Legitimate users denied service

Characteristics:

Floods servers with requests

Prevents legitimate users from accessing services

Can be extended as DDoS (Distributed DoS) using multiple systems

Example:

A website crashing due to too many fake requests.

Comparison Table

Feature	Virus	Worm	Trojan	DoS Attack
Spreads?	Yes (via files) boot sector	Yes (automatic)	No	Not applicable
User Action	Required, Network services	Not required	Required	Not required
Main Purpose	Damage data, Applications, users	Spread rapidly	Steal/control	Disrupt service
Self-Replicate	Yes, System resources	Yes	No	No

Simple Understanding

Virus → Needs a host file

Worm → Spreads on its own

Trojan → Disguised attacker

DoS → Overloads system

 

OS-Level Protection Mechanisms

To defend against these attacks, operating systems use:

User authentication & access control

Memory protection (process isolation)

File permissions

Firewalls & network filtering

Antivirus and intrusion detection systems

Regular security updates/patches

Simple Summary

Virus: Infects OS files and spreads via execution

Worm: Exploits OS/network to spread automatically

Trojan: Tricks OS into granting access

DoS: Overloads OS resources to stop services

Exam-Ready Answer (Short)

In an OS, threats like virus, worm, Trojan, and DoS attack system resources.

Virus infects files and spreads through execution

Virus: Attaches to files and spreads via user action

Worm: Self-replicating malware spreading over networks

Worm spreads automatically using OS vulnerabilities

Trojan: Malicious software disguised as legitimate

Trojan disguises as legitimate software to gain access

DoS: Attack that makes services unavailable by flooding traffic

DoS attack exhausts OS resources, denying services