🦠 Computer Viruses

Learn how computer viruses spread, infect files, and why virus concepts still matter in modern cybersecurity.

📼 A Blast From The Past

In the early days of computing, malware often spread through:

• Floppy disks
• CDs
• Email attachments
• Shared files

One infected file could spread to thousands of systems.

This type of malware became known as a virus.

📖 What Is A Computer Virus?

A virus is malicious software that attaches itself to another file or program.

Unlike worms:

Viruses Require User Action

The infected file must usually be opened, executed, or shared before the virus spreads.

🧬 Why It’s Called A Virus

The concept is similar to biological viruses spreading between hosts.

⚙️ Typical Virus Components

• Infection Mechanism
• Replication Logic
• Trigger Condition
• Payload

Not all viruses are destructive, but all attempt to spread.

🦠 Common Virus Types

• File Infector Viruses
• Boot Sector Viruses
• Macro Viruses
• Multipartite Viruses
• Polymorphic Viruses

Each type uses a different infection strategy.

📄 File Infector Viruses

These viruses attach themselves to:

• Programs
• Executables
• Application files

When the user launches the file, the virus executes as well.

📑 Macro Viruses

Macro viruses target documents containing automation features.

Examples:

• Word Documents
• Excel Spreadsheets
• Office Templates

They became extremely common through email attachments.

🥷 Polymorphic Viruses

Some viruses attempt to evade detection by changing their appearance.

Although behavior remains similar, the file may look different each time.

This challenged traditional signature-based detection systems.

⚠ Common Infection Indicators

• Unexpected file changes
• Slow performance
• Frequent crashes
• Missing files
• Unknown processes
• Disabled security software

These symptoms should always trigger investigation.

🛠 Virus Investigation Tools

• VirusTotal
• Windows Defender
• Process Explorer
• Autoruns
• Sysmon
• Event Viewer

These tools help analysts identify suspicious activity and persistence.

⚔ Virus vs Worm

🎓 CEH Exam Focus

Remember:

• Viruses require a host file
• Viruses typically need user interaction
• Viruses differ from worms
• Polymorphic viruses attempt evasion
• Macro viruses spread through documents

These are common CEH exam concepts.

🏆 Key Lesson

A virus succeeds because users unknowingly help it spread.

Technology matters.

User behavior matters even more.

Trust Carefully
Execute Carefully

🪱 Worms & Self-Propagating Malware

Learn how worms spread automatically across networks, why they can move so quickly, and how some of history’s largest cyber incidents were caused by self-propagating malware.