Computer Virus and Malware Notes for SSC Exams

Computer viruses and malware are asked in almost every SSC Computer Knowledge section. The questions are about the type of malware, how it spreads and how to protect a system. These computer virus and malware notes for SSC give you the types, the difference between a virus, a worm and a trojan, and practice questions. Read it with the Cyber Security and Cyber Crime Notes and Internet and Networking Notes notes.

What Is a Computer Virus?

• A computer virus is a harmful program that attaches itself to a file or program, spreads when the file is opened and damages data.
• A virus needs a host file and needs the user to run it.
• Malware (malicious software) is the general name for all harmful programs, such as viruses, worms, trojans, spyware and ransomware.
• The first computer virus for a personal computer was Brain (1986). Creeper (1971) was an experimental self-replicating program.

Types of Malware

Types of Viruses

• Boot sector virus: infects the boot sector of the disk and starts when the computer boots.
• File infector virus: attaches itself to executable files (.exe, .com).
• Macro virus: infects documents with macros, such as Word and Excel files. Melissa (1999) is an example.
• Polymorphic virus: changes its code every time to avoid detection.
• Resident virus: stays in the memory and infects files that are opened.
• Multipartite virus: infects both the boot sector and the files.

Virus vs Worm vs Trojan

Protection from Malware

• Install a good antivirus and keep it updated. Examples: Quick Heal, Norton, McAfee, Kaspersky, Avast.
• Use a firewall to block unauthorised access.
• Do not open unknown email attachments or click on suspicious links.
• Take regular backups of important data.
• Update the operating system and software with the latest patches.
• Do not download pirated software.

History of Computer Viruses

The word virus for computer programs was used by Fred Cohen in 1983. Because the history is asked in current affairs and computer questions, remember "Creeper = first experimental, Brain = first PC virus".

How Malware Spreads

• Email attachments and links in phishing emails.
• Pen drives and other removable storage.
• Downloads from untrusted or pirated websites.
• Infected websites and malicious advertisements (malvertising).
• Software that is not updated, because attackers use known weaknesses (vulnerabilities).
• Infected apps outside the official app stores.
• Networks and shared folders.

Signs That a Computer Is Infected

• The computer becomes slow or hangs often.
• Unknown programs, pop-ups or advertisements appear.
• Files go missing, become corrupted or change their names.
• The browser home page changes without your permission.
• The antivirus is turned off by itself.
• The computer sends emails or messages that you did not send.
• The hard disk or the network is busy for no reason.

Antivirus, Firewall and Other Defences

• Antivirus detection methods: signature-based (matches known virus patterns), heuristic (looks for suspicious behaviour) and behaviour-based.
• Quarantine is a safe folder where the antivirus keeps the infected files.
• A false positive is when a safe file is wrongly marked as a virus.

Other Threats Related to Malware

Important Questions Explained

Question 1: Which malware spreads by itself through a network without a host file?
Answer: A worm.

Question 2: Which malware looks like a useful software but harms the computer?
Answer: A Trojan horse.

Question 3: Which malware locks the files and asks for money?
Answer: Ransomware.

Question 4: Which virus attaches to Word or Excel documents?
Answer: A macro virus.

Question 5: Which software is used to detect and remove viruses?
Answer: Antivirus software.

Question 6: Which malware secretly collects the information of the user?
Answer: Spyware.

Quick Tips to Remember

• Learn the key difference: a virus needs a host, a worm does not and a trojan does not replicate.
• Link ransomware with money, spyware with spying and adware with advertisements.
• Remember a keylogger as the thief of passwords.
• Link firewall with blocking network threats and antivirus with removing viruses.
• Remember Brain as the first PC virus.

Common Mistakes to Avoid

• Writing a worm as a virus that needs a host.
• Saying that a trojan replicates itself.
• Mixing the firewall and the antivirus.
• Confusing spyware with adware.
• Thinking that all malware is a virus.

Quick Revision Points

• Malware = malicious software. Virus needs a host; worm spreads on its own; trojan is disguised.
• Ransomware asks for a ransom; spyware collects secret data.
• Antivirus removes viruses; firewall filters network traffic.
• Macro virus infects Word and Excel files.
• Brain (1986) was the first PC virus.

Practice Questions With Answers

1. A self-replicating program that does not need a host is?
   Answer: Worm (Spreads by networks).
2. A program that appears useful but is harmful is?
   Answer: Trojan horse (Does not replicate).
3. Which malware demands money to unlock files?
   Answer: Ransomware (WannaCry).
4. Which malware records keystrokes?
   Answer: Keylogger (Steals passwords).
5. Which software protects a computer from viruses?
   Answer: Antivirus (Must be updated).
6. Which security tool filters network traffic?
   Answer: Firewall (Hardware or software).
7. Unwanted advertisements are shown by?
   Answer: Adware (Pop-ups).
8. A virus that changes its code each time is?
   Answer: Polymorphic virus (Avoids detection).
9. Which virus infects the start-up of a disk?
   Answer: Boot sector virus (Active at boot).
10. A network of infected computers is called?
    Answer: Botnet (Controlled remotely).

More Practice Questions With Answers

1. Which was the first experimental self-replicating program?
   Answer: Creeper (1971).
2. Which worm spread in 2000 through email?
   Answer: ILOVEYOU (Email worm).
3. Which ransomware attacked in 2017?
   Answer: WannaCry (Bitcoin ransom).
4. Which attack uses a weakness before the maker knows it?
   Answer: Zero-day attack (Unknown vulnerability).
5. What is a safe folder for infected files called?
   Answer: Quarantine (Antivirus).
6. Which tool runs a suspicious file in an isolated area?
   Answer: Sandbox (Safe test).
7. What is a computer controlled by an attacker called?
   Answer: Zombie (Botnet).
8. Who first used the word virus for computer programs?
   Answer: Fred Cohen (1983).
9. Which detection method matches known patterns?
   Answer: Signature-based detection (Antivirus).
10. Which worm attacked industrial control systems?
    Answer: Stuxnet (2010).
11. What is a safe file marked as a virus called?
    Answer: False positive (Antivirus error).
12. Which virus is the first for IBM PCs?
    Answer: Brain (1986).

How to Practise This Chapter

1. Read the tables once and learn the key facts by heart.
2. Revise the quick revision points the next day.
3. Attempt the practice questions above without looking at the answers.
4. Solve a full SSC CGL Tier 1 mini mock to test your general awareness.
5. Check the previous year papers to see how SSC asks computer questions.

Related Notes and Practice Papers

• Cyber Security and Cyber Crime Notes
• Internet and Networking Notes
• Operating System Notes
• Computer Knowledge Notes for SSC
• SSC CGL Tier 1 Mini Mock

Explore More SSC Subjects

SSC exams test many subjects, so connect this topic with the related subjects below:

• General Science Notes
• General Awareness Notes
• Quantitative Aptitude Notes
• Reasoning Notes
• Electrical Engineering (SSC JE) Notes
• All SSC subjects and notes

Frequently Asked Questions

What is a computer virus?

A computer virus is a harmful program that attaches to files, spreads when they are opened and damages the data.

What is malware?

Malware means malicious software, a general term for harmful programs such as viruses, worms, trojans and spyware.

What is the difference between a virus and a worm?

A virus needs a host file to spread, while a worm spreads on its own through a network.

What is a Trojan horse?

A Trojan horse is a harmful program that looks like useful software but does not replicate itself.

What is ransomware?

Ransomware locks or encrypts the files of a user and demands money to unlock them.

What is spyware?

Spyware secretly collects information about the user without permission.

What does an antivirus do?

An antivirus detects, blocks and removes viruses and other malware.

What is a firewall?

A firewall is a security system that filters the network traffic and blocks unauthorised access.

How many questions come from viruses in SSC exams?

One or two questions usually come from viruses, malware and security.

What is the difference between antivirus and firewall?

An antivirus finds and removes harmful programs on the computer, while a firewall filters the network traffic and blocks unauthorised access.

What is a zero-day attack?

A zero-day attack uses a software weakness that is not yet known to the maker, so there is no patch for it.

How can I protect my computer from malware?

Use a trusted antivirus, keep software updated, avoid unknown links and attachments, use a firewall and keep backups.