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Types of viruses and other malware

Malware is the umbrella word for any malicious software. A virus is one family; worms, trojans and ransomware are others. Knowing the type tells you how it spreads and how to stop it.

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Classic virusesFile viruses infect programs, boot-sector viruses load before the OS (Brain, Michelangelo), macro viruses ride inside Office documents (Melissa, 1999).
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Polymorphic & stealthChange their own code on every copy or hide from the operating system, so signature-only antivirus misses them.
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WormSpreads on its own across networks without a host file or a click: Morris (1988), SQL Slammer (2003), WannaCry (2017).
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TrojanPretends to be useful (a game, a “bank” APK, a wedding-invitation file) so you install it yourself. Banking trojans like CyberDakait (2026) read your SMS to steal OTPs.
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RansomwareEncrypts your files and demands payment, often stealing the data first to threaten a leak: CryptoLocker, WannaCry, the 2026 hospital attacks.
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Spyware & adwareSpyware and keyloggers record what you type and where you go; adware floods you with pop-ups and redirects your browser.
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Rootkit & botRootkits hide deep in the operating system to keep an attacker's access; bots make your device part of a botnet used for spam and DDoS (Mirai, 2016).
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Fileless & cryptojackingFileless malware runs only in memory using built-in tools; cryptojackers secretly mine cryptocurrency on your machine.
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Mobile malwareFake apps that ask for SMS, call or accessibility permissions, then drain accounts. Official stores and permission checks stop most of them.
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Tip: press → or Space to step through, ← to go back, R to replay.

About this lesson

Malware is any software written to harm or exploit a device, and viruses are only one family within it. Classic virus types are named after where they hide: file infectors, boot-sector viruses, macro viruses inside Office documents, and polymorphic or stealth viruses that change their code to evade antivirus signatures. Worms spread by themselves across networks, trojans disguise themselves as useful apps, ransomware encrypts files for payment, spyware and keyloggers record what you do, adware pushes advertisements, rootkits hide an attacker's access, and bots turn devices into botnet soldiers. On phones the main danger is fake apps delivered as APK files through chat apps that request SMS and accessibility permissions. Each type has a matching defence, which the full Phase 2 covers along with antivirus software and device hygiene.

Key points

  • File, boot-sector, macro and polymorphic viruses
  • Worms, trojans and ransomware
  • Spyware, adware, rootkits, botnets and mobile malware