What Are the Most Common Types of Malware?

Introduction

Cybercriminals deployed over 1.2 billion new malware samples in 2024 alone. Ransomware payments hit $1.1 billion. One in three organizations faced a malware attack last year. From stealthy fileless scripts to AI-powered phishing, malware isn't just growing. It's getting smarter.

This guide breaks down the 12 most common malware types in 2025. You'll learn how each works, real-world examples, infection vectors, and proven defenses. Whether you're an IT admin, developer, or home user, understanding these threats is your first line of defense. Let's dive in.

Ransomware: The Digital Extortion King

Ransomware encrypts files and demands payment for decryption. It’s the most profitable malware, with groups like LockBit and BlackCat dominating headlines. Attacks now use double extortion: encrypt and leak.

• Encrypts documents, databases, backups
• Demands Bitcoin or Monero
• Examples: WannaCry (2017), Colonial Pipeline (2021)
• Spreads via phishing, RDP, exploits
• Prevention: offline backups, patch management
• Never pay. Report to authorities

Trojans: Masters of Deception

Trojans masquerade as legitimate software to trick users into installation. Once inside, they open backdoors, steal data, or download more malware. Emotet was the most widespread trojan in 2024.

• Disguised as games, PDFs, cracks
• Creates remote access for attackers
• Steals banking credentials, emails
• Spreads via spam, drive-by downloads
• Use reputable sources only
• Scan attachments with VirusTotal

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Spyware: Silent Data Thieves

Spyware monitors user activity without consent. It logs keystrokes, captures screenshots, and tracks browsing. Pegasus by NSO Group infected thousands of journalists and activists.

• Records passwords, messages, calls
• Uses camera and microphone
• Zero-click exploits (iMessage, WhatsApp)
• Installed via apps, browser extensions
• Update OS and apps immediately
• Avoid jailbreaking/rooting

Adware: Annoying but Dangerous

Adware bombards users with unwanted ads. While often bundled with free software, malicious adware redirects to phishing sites or installs more malware.

• Injects ads into browsers
• Changes homepage, search engine
• Tracks browsing for targeted ads
• Comes with "free" tools, games
• Uninstall suspicious programs
• Use ad blockers (uBlock Origin)

Rootkits: The Invisible Threat

Rootkits hide deep in the OS, masking malware presence. They modify system files to evade detection. Sony BMG’s 2005 rootkit sparked global outrage.

• Intercepts system calls
• Hides processes, files, registry keys
• Kernel-mode rootkits hardest to detect
• Requires boot-time scanning
• Use GMER, RootkitRevealer
• Reinstall OS if infected

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Worms: Self-Replicating Nightmares

Worms spread autonomously across networks without user interaction. ILOVEYOU (2000) infected 50 million PCs in 10 days. Modern worms exploit zero-days.

• Scans for vulnerable systems
• Uses SMB, email, USB
• Consumes bandwidth, installs backdoors
• Patch vulnerabilities fast
• Segment networks
• Disable autorun

Botnets: Armies of Zombie Devices

Botnets are networks of infected devices controlled by a command server. Mirai turned IoT devices into a 1 Tbps DDoS weapon in 2016.

• Launches DDoS, spam, click fraud
• Infects routers, cameras, PCs
• Uses IRC or HTTP C2
• Change default passwords
• Update firmware
• Monitor outbound traffic

Fileless Malware: Living in Memory

Fileless malware runs in RAM, leaving no disk traces. It uses legitimate tools (PowerShell, WMI) to execute. 77% of successful attacks in 2024 were fileless.

• Exploits living-off-the-land (LotL)
• No executable to scan
• Uses macros, scripts, registry
• Enable AMSI (Windows)
• Restrict PowerShell
• Monitor behavior, not signatures

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Cryptojackers: Stealing Your CPU

Cryptojackers mine cryptocurrency using victim devices. Coinhive infected 500 million users via browser scripts before shutting down.

• Runs in background, slows system
• Web-based (drive-by mining)
• Malicious apps, extensions
• Block JavaScript with NoScript
• Use anti-cryptojacking extensions
• Monitor CPU usage

Keyloggers: Every Keystroke Counts

Keyloggers record everything you type. Hardware keyloggers plug between keyboard and PC. Software ones hide in free apps.

• Captures passwords, credit cards
• Physical or remote access
• Uses clipboard hijacking
• Use on-screen keyboards for sensitive input
• Scan with Malwarebytes, SpyBot
• Check USB devices

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Wipers: Digital Destruction

Wipers permanently delete or corrupt data. NotPetya (2017) caused $10 billion in damage, disguised as ransomware but designed to destroy.

• Overwrites MBR, files, logs
• Nation-state attacks (Shamoon)
• No recovery without backups
• Air-gap critical systems
• Test backups regularly
• Use write-once media

Mobile Malware: Phones Are Targets Too

Mobile malware grew 500% since 2020. Joker, Anatsa, and Sharkbot steal banking credentials via overlay screens.

• Fake apps on third-party stores
• SMS premium scams
• Rooting exploits
• Install from Google Play/Apple Store only
• Enable Play Protect
• Avoid sideloading

Malware Infection Vectors Comparison

Conclusion

Malware isn’t going away. But neither are you. Patch systems, train users, backup data, and layer defenses. One weak link invites attack. Twelve strong ones stop it cold.

Start simple: update everything, enable MFA, scan regularly. In 30 days, your risk drops 90%. Stay vigilant. Stay safe.

Frequently Asked Questions

What is the most dangerous malware type?

Ransomware. It encrypts data and demands payment, with no guarantee of recovery.

Can antivirus detect all malware?

No. Fileless, zero-day, and polymorphic malware often evade signature-based AV.

Is free antivirus enough?

For home users, yes (Windows Defender, Avast). Enterprises need EDR.

How do I remove stubborn malware?

Boot into Safe Mode, use Malwarebytes, or reinstall OS.

Can malware infect external drives?

Yes. Worms and trojans spread via USB. Scan before opening.

Is Mac immune to malware?

No. macOS malware (XLoader, Atomic) is rising. Use Gatekeeper and XProtect.

What’s the difference between virus and worm?

Virus needs user action. Worm spreads automatically.

Can malware survive factory reset?

Rarely. But firmware malware (LoJax) can. Flash BIOS if suspected.

How to spot cryptojacking?

High CPU, slow performance, fan noise when idle.

Should I pay ransomware?

No. 92% of payers lose data anyway. Report to FBI/IC3.

Is mobile antivirus necessary?

Not on iOS. On Android, yes (Google Play Protect + Malwarebytes).

Can malware steal passwords from password managers?

Only if you’re infected with a keylogger and enter the master password.

What is polymorphic malware?

Malware that changes code signature to evade detection.

How often should I scan for malware?

Weekly full scan. Real-time protection always on.

What’s the best defense against malware?

User education + patching + backups + EDR.