Malware Types: Viruses, Worms, Trojans, Ransomware, Spyware & Adware

This lesson provides an in-depth look at the different types of malware you need to know for OCR J277 Section 1.4. Each type has distinct characteristics, methods of spreading, and impacts.

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What Is Malware?

Malware is a general term for any software that is intentionally designed to cause damage to a computer, server, client or computer network. The word comes from "malicious software."

Malware can:

• Steal sensitive data (passwords, financial information)
• Encrypt files and demand ransom
• Spy on user activity
• Damage or delete files
• Use system resources for malicious purposes (e.g. cryptocurrency mining, botnets)

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Viruses

A computer virus is a piece of malicious code that attaches itself to a legitimate program or file. It requires human action to spread — the infected file must be opened, run, or shared.

Characteristics of viruses:

• Attach to host files (documents, programs, macros)
• Replicate by copying themselves into other files when the host is executed
• Can be dormant until triggered (e.g. on a specific date)
• Spread via email attachments, USB drives, file downloads

Feature	Detail
Needs host file	Yes
Needs user action	Yes — user must open/run the file
Self-replicating	Only when host is executed
Spread method	Email, USB, downloads

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Worms

A worm is a standalone malicious program that replicates itself to spread to other computers. Unlike viruses, worms do not need a host file and do not require user action to spread.

How worms spread:

1. A worm exploits vulnerabilities in software or operating systems.
2. Once on a system, it automatically scans for other vulnerable machines on the network.
3. It copies itself to those machines and repeats the process.

Worms can spread extremely quickly across networks, consuming bandwidth and processing power. They can also carry a payload that performs additional malicious actions.

OCR Exam Tip: The key difference between a virus and a worm is that a worm is self-replicating and does NOT need a host file or user action. This is a very common comparison question in the exam.

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Trojans

A trojan (short for Trojan horse) is malware that disguises itself as legitimate or useful software to trick users into installing it.

Characteristics of trojans:

• Do not self-replicate (unlike viruses and worms)
• Rely on social engineering — the user willingly installs them
• Once installed, they can create backdoors for remote access, steal data, or download additional malware
• Often bundled with free software, games, or pirated content