Computer Virus – JSS3 Computer Studies Lesson Note (Third Term)

A computer virus is a malicious program that copies itself from one file or computer to another and damages data and software.

• Malware: short for malicious software, the general name for harmful programs.
• Virus: a program written by a malicious programmer to harm a computer system.
• Effects: viruses disrupt systems, cause operational problems and lead to data loss and leakage.

Behavioural objectives

By the end of the lesson, students should be able to:

1. define a computer virus;
2. describe four types of computer virus;
3. name some examples of computer viruses;
4. list common sources of computer viruses;
5. state signs of an infected computer and ways to prevent infection.

What is a computer virus?

A computer virus is a type of malware that attaches itself to a program or file and spreads when that file is opened or run.

• Self-copying: it makes copies of itself and moves to other files and computers.
• Needs a host: it hides inside a program, document or the boot area of a disk.
• Harmful: it can delete, corrupt or steal data and slow down the system.
• Spread by people: it travels through shared disks, downloads, email and networks.

What are the types of computer virus?

There are four main types of computer virus: boot sector virus, executable file virus, multipartite virus and macro virus.

1. Boot sector virus

• Meaning: a virus that infects a system’s boot partition or the master boot record (MBR) of a hard disk.
• Effect: it loads into memory when the computer starts.
• Common source: an infected diskette, flash drive or CD-ROM left in the computer during start-up.

2. Executable file virus

• Meaning: a virus that infects executable and command files of application packages.
• Spread: infected applications pass the virus to associated documents and other applications whenever they are opened or run.
• Other name: it is also called a file virus.

3. Multipartite virus

• Meaning: a fast-acting virus that attacks a device’s boot sector and executable files at the same time.
• Danger: it is often considered more problematic than traditional viruses because it can spread in multiple ways.

4. Macro virus

• Meaning: a virus written in a macro language, which is a programming language embedded inside a software application.
• Target: documents and spreadsheets, such as those made in word processors.
• Spread: it runs when an infected document is opened and the macro is allowed to run.

What is the difference between a boot sector virus and a multipartite virus?

A boot sector virus infects only the start-up area of a disk, while a multipartite virus infects both the boot sector and executable files.

What are examples of computer viruses?

Examples of well-known computer viruses and related malware are listed below.

• Morris Worm: an early program that spread across networks.
• Trojan horse: a harmful program that pretends to be useful software.
• Jerusalem virus: a virus that infects executable files.
• Christmas/25th December virus: a virus linked to a particular date.
• Alabama virus: a virus that infects executable files.
• ILOVEYOU: a virus that spread by email.
• Ping-Pong virus: a boot sector virus.
• SQL Slammer: a program that spread quickly across networks.
• Stuxnet: a program that attacked industrial control systems.
• CryptoLocker: a program that locks files until money is paid (ransomware).
• Conficker: a program that spread across networks.
• Tinba: a program that steals banking details.
• Logic bomb: harmful code that runs when a set condition is met.
• Sleeper virus: a virus that stays hidden until it is triggered.

What are the other kinds of malware?

Malware is any program made to harm a computer or steal information, and a virus is only one kind.

What are the sources of computer viruses?

Computer viruses come from infected storage devices, unsafe downloads, illegal software and email or wireless transfers.

• Infected diskette: a shared diskette can carry a virus to the next computer.
• Booting from an infected CD-ROM: the virus loads as the computer starts.
• Illegal duplication: copying software without permission can copy the virus too.
• Unsecured downloading: files from unknown websites may hide a virus.
• Sharing of external storage devices: flash drives and external hard disks pass viruses between computers.
• Infected memory card: a card used in many phones and cameras can carry a virus.
• Pirated or cracked software: illegal copies may contain hidden malware.
• Unpatched software: programs that are not updated keep security weaknesses that viruses use.
• Email attachments: opening an unknown attachment can run a virus.
• Bluetooth: files received from unknown devices may be infected.

What are the signs of a computer virus?

The signs of a computer virus are strange behaviour such as slow performance, missing files and unwanted messages.

• Slow computer: programs take longer than usual to open.
• Missing or damaged files: files disappear, change name or cannot be opened.
• Strange messages: unwanted pop-ups or error messages appear.
• Unexpected restarts: the computer shuts down or restarts without a command.
• Programs acting alone: programs open or close by themselves.
• Disabled antivirus: the antivirus program stops working.

How can we prevent computer viruses?

Computer viruses are prevented by installing antivirus software, updating programs and avoiding unsafe files and devices.

1. Install an antivirus program and keep it updated.
2. Scan every flash drive, diskette and memory card before opening it.
3. Do not open email attachments from unknown senders.
4. Download files only from trusted websites.
5. Do not use pirated or cracked software.
6. Update the operating system and other programs regularly.
7. Back up important files on a separate device.

What is an antivirus program?

An antivirus program is software that detects, blocks and removes viruses and other malware.

• Scanning: it checks files and disks for known viruses.
• Removal: it deletes the virus or places infected files in quarantine.
• Updates: it must be updated often so that it can detect new viruses.
• Examples: Windows Defender, Avast, AVG, Kaspersky, Norton and Bitdefender.

Evaluation

1. What is a computer virus?
2. Name four types of computer virus.
3. What is the difference between a boot sector virus and a multipartite virus?
4. Give three examples of computer viruses.
5. List four sources of computer viruses.

Assignment

1. Describe a macro virus and an executable file virus.
2. List five ways a computer can get a virus.