A computer virus is a malicious program designed to harm or disrupt computers, steal data, or gain unauthorized access. There are many types of computer viruses, each with unique behavior and impact.

1. File Infectors

• What They Do:
  Infect executable files (e.g., .exe or .dll) and spread when the program runs.
• Example: Cascade Virus.
• Impact: Slows system performance, corrupts programs, or deletes files.

2. Macro Viruses

• What They Do:
  Target software with macro functionality, such as Microsoft Office (Word, Excel).
• Example: Melissa Virus.
• Impact: Alters or deletes documents and spreads via infected files or emails.

3. Boot Sector Viruses

• What They Do:
  Infect the master boot record (MBR) or boot sector of storage drives.
• Example: Michelangelo Virus.
• Impact: Prevents the system from starting or causes boot issues.

4. Polymorphic Viruses

• What They Do:
  Alter their code to avoid detection by antivirus programs.
• Example: Storm Worm.
• Impact: Hard to detect and remove, causes significant damage.

5. Resident Viruses

• What They Do:
  Embed themselves into a computer’s memory, activating whenever the system runs.
• Example: Randex Virus.
• Impact: Infects files, disrupts operations, and slows down the system.

6. Worms

• What They Do:
  Spread through networks without infecting files. Worms exploit security flaws to replicate themselves.
• Example: Mydoom Worm.
• Impact: Overloads networks, causes crashes, and consumes bandwidth.

7. Trojan Horses (Trojans)

• What They Do:
  Disguise themselves as legitimate programs but execute malicious activities.
• Example: Zeus Trojan.
• Impact: Steals sensitive data, like passwords or financial information.

8. Ransomware

• What They Do:
  Encrypt files and demand payment for their release.
• Example: WannaCry.
• Impact: Data loss or financial extortion.

9. Spyware

• What They Do:
  Secretly monitors user activity and collects sensitive information.
• Example: CoolWebSearch.
• Impact: Invades privacy and steals personal data.

10. Adware

• What They Do:
  Automatically delivers unwanted ads, often bundled with free software.
• Example: Fireball.
• Impact: Annoying pop-ups, slow performance, and potential data collection.

11. Keyloggers

• What They Do:
  Record keystrokes to steal login credentials or personal information.
• Example: Invisible Keylogger.
• Impact: Compromises accounts and sensitive data.

12. Logic Bombs

• What They Do:
  Trigger malicious actions when specific conditions are met.
• Example: Time Bomb.
• Impact: Deletes files, crashes systems, or steals data when activated.

How to Protect Against Viruses

1. Install and update reputable antivirus software.
2. Avoid clicking on suspicious links or downloading untrusted files.
3. Regularly update your operating system and software.
4. Use strong passwords and enable two-factor authentication.
5. Back up your data frequently.

Understanding these virus types can help you stay alert and protect your system effectively