Lesson 9 of 10 – Computer Virus
90%
90%

Computer Virus

A computer virus is a harmful program or piece of code that can damage files, slow down the computer, and interfere with normal working.

Viruses usually enter a computer through infected files, downloads, email attachments, USB drives, or networks. Once inside, they can copy themselves and spread to other files or systems.

Simple meaning: A computer virus is like a digital illness that can harm your computer system.

What is a Computer Virus?

Computer viruses are unwanted software programs or pieces of code that interfere with the functioning of the computer. They spread through infected files, data, removable drives, and networks. Many viruses are designed to copy themselves and infect other files.

How Does a Virus Spread?

Infected Files

When a user opens or downloads an infected file, the virus may enter the computer and begin spreading.

Email Attachments

A virus can hide inside an email attachment and infect the computer when the file is opened.

USB / Pen Drive

Infected pen drives and storage devices can transfer viruses from one computer to another.

Internet and Networks

Viruses can also spread through unsafe websites, downloads, and connected networks.

Types of Computer Virus

Overwrite Virus

An overwrite virus destroys original file data and replaces it with its own code. The infected file may become unusable.

Append Virus

An append virus attaches itself to the end of a file and changes its original content.

Macro Virus

A macro virus infects documents that contain macros, such as Word or Excel files.

Boot Virus

A boot virus infects the boot sector of a storage device. It starts working when the computer boots.

Resident Virus

A resident virus stays in memory after the computer starts and can infect files continuously.

Non-resident Virus

A non-resident virus does not stay in memory. It infects files for a short time and then stops.

File Infector Virus

A file infector virus attacks executable files and spreads when those files are opened.

Computer Worm

A worm is a harmful program that spreads from one computer to another without needing a host program.

Trojan Horse

A Trojan horse is malicious software that looks safe but is actually dangerous. It tricks users into installing it.

Polymorphic Virus

A polymorphic virus changes its form or code to avoid detection by antivirus software.

Symptoms of Computer Virus

A virus may show some warning signs. If your computer behaves strangely, it may be infected.

  • Slow performance
  • Frequent pop-ups
  • System crashes
  • Unknown programs appearing on the computer
  • Network issues
  • Strange messages
  • Display problems
  • Files getting damaged or missing

How to Protect a Computer from Virus

  • Install antivirus software
  • Do not open unknown email attachments
  • Avoid unsafe websites
  • Scan pen drives before using them
  • Keep your operating system updated
  • Do not download suspicious files
💡 Remember
A computer virus is harmful software that can damage files and slow down the system. Safe browsing, antivirus protection, and careful downloading help prevent virus attacks.

🧠 Quiz

Which virus infects the boot sector?