What Is Malware? Types, Signs & Protection (2026)

Malware ("malicious software") is any program built to harm, exploit, or gain unauthorized access to a device or network. It's the umbrella term that covers viruses, worms, trojans, ransomware, spyware, and more. Here's how it works and how to defend.

The main types

• Virus — attaches to files/programs and spreads when they run.
• Worm — self-replicating; spreads across networks on its own.
• Trojan — disguised as something legitimate; you install it yourself.
• Ransomware — encrypts your files and demands payment.
• Spyware / Keyloggers — secretly record your activity and credentials.
• Adware — floods you with ads; often bundled with worse.
• Rootkits — hide deep in the system to evade detection.
• Botnet malware — turns your device into part of an attacker's network.

How it spreads

• Phishing emails and malicious attachments (the #1 route).
• Malicious downloads — cracked software, fake installers.
• Drive-by downloads from compromised sites.
• USB drives and removable media.
• Unpatched vulnerabilities — see the CVE tracker.

Warning signs

• Sudden slowness, crashes, or overheating.
• Unknown programs, pop-ups, or browser changes.
• Unusual network activity or disabled security tools.
• Files renamed/encrypted (a ransomware tell).

How to protect yourself

1. Patch everything — most malware exploits known, unpatched bugs.
2. Use reputable antivirus/EDR and keep it updated.
3. Don't run untrusted files — think before you open attachments or install software.
4. Least privilege — don't run as admin day-to-day.
5. Back up — offline/immutable backups defeat ransomware.
6. MFA — limits the damage if credentials are stolen.

If you're infected

Disconnect from the network, don't pay blindly, run a reputable scanner, change passwords from a clean device, and restore from backup if needed. For organizations, follow your incident-response plan.

Understanding how malware gets in is the first step to keeping it out. Learn attacker techniques (to defend against them) free at the Pentevo Academy.