What Is Malware? 12 Types of Malware Explained with Examples

Malware, short for malicious software, is any program or code designed to damage, disrupt, or gain unauthorised access to a computer system. The main types of malware include viruses, worms, trojans, ransomware, spyware, adware, rootkits, keyloggers, botnets, fileless malware, wipers, and cryptojackers. Each type works differently, spreads differently, and causes a distinct kind of harm.

• Key Takeaway 1: Malware is a broad category. A virus is just one type, not a synonym for all malware.
• Key Takeaway 2: AV-TEST Institute registered over 450,000 new malicious programs every single day as of its 2024 Security Report.
• Key Takeaway 3: Phishing emails and malicious downloads are the two most common infection vectors worldwide.
• Key Takeaway 4: Some malware, like fileless malware, leaves no files on disk and bypasses traditional antivirus entirely.
• Key Takeaway 5: Understanding malware types is the first practical step toward a career in cybersecurity or malware analysis.

What Is Malware and How Does It Infect a Computer?

Malware infects a computer through several well-documented vectors. According to Verizon’s 2024 Data Breach Investigations Report (DBIR), phishing accounts for the largest share of initial access in confirmed breaches, followed by exploitation of public-facing applications and use of stolen credentials. Drive-by downloads, malicious email attachments, infected USB drives, and compromised software updates are also common entry points.

Once inside a system, malware executes its payload. That payload might encrypt your files, steal your passwords, spy on your activity, or quietly recruit your machine into a global botnet. The delivery method and the payload are often separate, which is why the same phishing email can drop a dozen different malware families depending on what the attacker wants.

India has seen this first-hand. The 2022 AIIMS Delhi ransomware attack paralysed the hospital’s servers for nearly two weeks, affecting patient records and forcing staff to revert to manual processes. CERT-In, India’s national cybersecurity agency, responded with an advisory and coordinated the recovery effort. It is a clear example of how a single infection can cascade into a national-level incident.

If you want to understand how phishing attacks deliver malware, 3.0 University’s dedicated guide breaks down the mechanics in plain language.

12 Types of Malware Explained with Real Examples

1. Virus

A virus attaches itself to a legitimate file or program. When that file runs, the virus executes and replicates by injecting its code into other files. It needs a human action, like opening an infected document, to spread. The ILOVEYOU virus of 2000 infected over 50 million computers within ten days, causing an estimated $10 billion in damage, according to the FBI.

2. Worm

A worm spreads on its own without needing a host file or user interaction. It exploits network vulnerabilities to copy itself from machine to machine. The WannaCry worm in 2017 hit over 200,000 systems across 150 countries in a single weekend, including the UK’s NHS. Worms are faster and harder to contain than viruses because they do not wait for anyone to click anything.

3. Trojan

A trojan disguises itself as legitimate software. You install what looks like a free game or a cracked utility, and the trojan installs alongside it without your knowledge. It does not self-replicate, but it opens backdoors, steals data, or downloads additional malware. The Zeus trojan, active from around 2007, stole banking credentials from millions of users globally.

4. Ransomware

Ransomware encrypts your files and demands payment for the decryption key. It is one of the most financially damaging malware types in operation today. According to Cybersecurity Ventures’ 2022 Cybercrime Report, global ransomware damages were projected to hit $265 billion annually by 2031. The 2021 Colonial Pipeline attack in the US shut down fuel supply to the East Coast and the attackers received $4.4 million before the FBI recovered a portion of it.

5. Spyware

Spyware silently monitors user activity and sends the data back to a remote attacker. It can capture browsing history, login credentials, and even activate a device’s camera or microphone. Pegasus, developed by NSO Group, is arguably the most sophisticated spyware ever documented. It was used to target journalists, activists, and government officials in multiple countries, including India, according to findings by Amnesty International’s Security Lab in 2021.

6. Adware

Adware bombards users with unwanted advertisements, often redirecting browsers to affiliate pages to generate revenue for the attacker. On its own, adware is more annoying than destructive. The problem is that many adware packages bundle spyware or download more dangerous payloads once installed. Superfish, pre-installed on Lenovo laptops in 2015, was a high-profile adware case that also created a serious SSL vulnerability.

7. Rootkit

A rootkit hides deep inside an operating system, often at the kernel level, to conceal the presence of other malware. It is specifically built to evade detection. The Sony BMG rootkit scandal of 2005 is a textbook case: Sony secretly installed rootkit software on millions of CDs that hid itself on Windows machines to enforce copy protection, and it left those machines open to further exploitation.

8. Keylogger

A keylogger records every keystroke a user makes, capturing passwords, credit card numbers, and private messages. Hardware keyloggers plug into a keyboard port; software keyloggers run invisibly in the background. They are a favoured tool of both state-sponsored threat actors and cybercriminals running banking fraud operations. Multiple Indian banking fraud cases investigated by CERT-In have involved keylogger components, as noted in CERT-In’s annual threat landscape advisories.

9. Botnet

A botnet is a network of infected machines, called bots or zombies, controlled remotely by an attacker. The attacker uses the combined computing power for spam campaigns, distributed denial-of-service (DDoS) attacks, or cryptocurrency mining. The Mirai botnet in 2016 recruited hundreds of thousands of IoT devices and used them to knock major websites offline, including Twitter and Netflix, in a massive DDoS attack.

10. Fileless Malware

Fileless malware does not write files to disk. Instead, it lives entirely in memory, using legitimate system tools like PowerShell or Windows Management Instrumentation to execute its payload. Because there is no file to scan, traditional antivirus tools often miss it entirely. According to the Ponemon Institute’s 2020 State of Endpoint Security Risk Report, fileless attacks are ten times more likely to succeed than file-based attacks.

11. Wiper

A wiper’s sole purpose is to permanently destroy data. There is no ransom demand, no espionage. It just deletes or corrupts everything it can reach. NotPetya in 2017 was initially disguised as ransomware but was actually a wiper. It caused over $10 billion in global damage, according to a White House assessment, and crippled companies like Maersk and Merck.

12. Cryptojacker

Cryptojacking malware hijacks a victim’s CPU and GPU to mine cryptocurrency for the attacker. The victim sees no ransom demand and no data theft, just a dramatically slower machine and a higher electricity bill. CoinHive, before it shut down in 2019, was embedded in thousands of websites and mined Monero using visitors’ browsers without consent.

If you are serious about analysing these threats professionally, read 3.0 University’s full guide on how to become a malware analyst to understand the skills, tools, and career path involved.

Quick Comparison: 12 Types of Malware at a Glance

Malware Type	Needs Host File?	Self-Replicates?	Primary Payload	Detection Difficulty	Famous Example
Virus	Yes	Yes	File corruption	Medium	ILOVEYOU (2000)
Worm	No	Yes	Network congestion, payload delivery	Medium	WannaCry (2017)
Trojan	Yes (disguised)	No	Backdoor, data theft	Medium	Zeus (2007)
Ransomware	No	Sometimes	File encryption, extortion	Medium	Colonial Pipeline (2021)
Spyware	No	No	Credential theft, surveillance	High	Pegasus (2016-present)
Adware	No	No	Unwanted ads, browser hijack	Low	Superfish (2015)
Rootkit	No	No	Concealment of other malware	Very High	Sony BMG (2005)
Keylogger	No	No	Keystroke capture, credential theft	High	Various banking fraud cases
Botnet	No	Yes	DDoS, spam, crypto mining	High	Mirai (2016)
Fileless Malware	No	No	Memory-based code execution	Very High	PowerShell-based attacks
Wiper	No	No	Permanent data destruction	Medium	NotPetya (2017)
Cryptojacker	No	No	CPU/GPU hijack for crypto mining	Medium	CoinHive (2017-2019)

How to Know If Your Device Has Malware and How to Protect It

Signs Your Device May Be Infected

Your device is likely compromised if you notice any of these: unexplained slowdowns or crashes, programs launching without your input, browser settings changing on their own, unknown processes consuming CPU or RAM, contacts reporting strange messages sent from your accounts, or files you did not delete going missing.

Mobile malware is an especially fast-growing problem. According to Kaspersky’s Mobile Virusology Report 2023, the company detected over 1.6 million malicious installation packages targeting Android devices in a single year. India, with its massive Android user base, is among the most targeted markets globally. The Data Security Council of India (DSCI) has separately noted that mobile-based cyber threats are among the fastest-growing attack categories affecting Indian consumers.

Practical Malware Protection Steps

• Keep your operating system and all applications patched and up to date. Most successful exploits target known vulnerabilities that already have patches available.
• Use an Endpoint Detection and Response (EDR) tool rather than relying solely on traditional antivirus. EDR tools catch behavioural anomalies that signature-based scanners miss.
• Enable multi-factor authentication on every account that supports it. Even if a keylogger steals your password, MFA adds a second barrier.
• Do not download cracked software or pirated media. These are among the most reliable delivery vehicles for trojans and adware.
• Back up your data regularly, ideally following the 3-2-1 rule: three copies, on two different media types, with one stored offsite or in the cloud.
• Train yourself to recognise phishing attempts. Social engineering is the attacker’s preferred first step before any malware is ever deployed.

For a deeper look at how endpoint tools defend against these threats, 3.0 University’s guide on what is endpoint security explains the technology in practical terms.

Malware vs Ransomware: Clearing Up the Confusion

Ransomware is a type of malware, not a separate category. The confusion is understandable because ransomware gets its own headlines and its own insurance products. But structurally, ransomware is malware with a specific payload: file encryption combined with a ransom demand. Every ransomware attack is a malware attack. Not every malware attack is ransomware.

Antivirus vs EDR: Which One Do You Actually Need?

Traditional antivirus compares files against a database of known malware signatures. It is still useful for catching commodity threats. EDR tools watch behaviour in real time, looking for suspicious patterns like a process injecting code into memory or a script running from an unusual directory. Against fileless malware, zero-day exploits, and advanced persistent threats, EDR is the more capable tool. For most individuals and small businesses, a reputable antivirus with behavioural detection features is a reasonable starting point.

Malware Analysis as a Career Path

Demand for professionals who can reverse-engineer malware and trace attack chains is genuinely outpacing supply. CERT-In regularly publishes advisories that depend on malware analysis work. Private sector demand is strong too, across banking, telecom, and critical infrastructure sectors in India. Skills in static and dynamic malware analysis, sandboxing, and threat intelligence are the core building blocks of this specialisation.

If you are exploring this path, 3.0 University’s course on threat hunting, digital forensics, and malware analysis covers the technical skills you need to get started.

Frequently Asked Questions

What are the main types of malware?

The main types of malware are viruses, worms, trojans, ransomware, spyware, adware, rootkits, keyloggers, botnets, fileless malware, wipers, and cryptojackers. Each has a distinct method of infection, propagation, and payload. Most real-world attacks combine more than one type. A trojan, for example, may deliver ransomware after establishing a foothold on the system.

What is the difference between a virus and malware?

Malware is the broad term for any malicious software. A virus is one specific type of malware that attaches itself to a host file and replicates when that file is executed. All viruses are malware, but not all malware is a virus. Worms, trojans, ransomware, and spyware are all malware but they are not viruses.

How do I know if my device has malware?

Common signs include unexpected slowdowns, crashes, programs launching on their own, browser redirects, unfamiliar processes in Task Manager, contacts receiving strange messages from you, and files disappearing. Some malware, especially spyware and fileless malware, shows no visible symptoms at all. Running a reputable security scan and monitoring network traffic are the most reliable detection methods.

Which malware is most dangerous?

Wipers and ransomware cause the most immediate, irreversible damage. NotPetya, a wiper, caused over $10 billion in global damage in 2017 according to the White House. Spyware like Pegasus is arguably the most dangerous from a privacy and national security standpoint. Fileless malware is the hardest to detect and remove. The most dangerous type depends on context: financial loss, data loss, or surveillance risk.

How does malware infect a computer?

Malware most commonly enters through phishing emails with malicious attachments or links, drive-by downloads from compromised websites, infected USB drives, unpatched software vulnerabilities, and malicious apps downloaded from unofficial sources. According to Verizon’s 2024 Data Breach Investigations Report, phishing and exploitation of vulnerabilities account for the majority of confirmed breach entry points globally.

What are the most common types of malware affecting Indian users?

Ransomware, spyware, and mobile trojans are among the most frequently reported malware types affecting Indian organisations and consumers. CERT-In advisories have highlighted ransomware attacks on critical infrastructure, including the 2022 AIIMS Delhi incident, as well as keylogger-based banking fraud and Pegasus-linked spyware targeting Indian nationals. Android-based malware is a growing concern given India’s large smartphone user base.

Last updated: July 2026. Reviewed by the 3University editorial team.