Malware is a broad term for malicious software, but different types behave differently: a virus attaches to legitimate files and spreads when they're shared, a worm spreads automatically across networks without needing a host file, a trojan disguises itself as legitimate software to trick users into installing it, spyware secretly monitors activity, and ransomware encrypts a victim's files and demands payment for the decryption key. Warning signs of infection include a sudden slowdown in performance, unexpected pop-ups, programs launching on their own, or unfamiliar files encrypted with strange extensions. Ransomware attacks typically begin with a phishing email or an unpatched software vulnerability, which is why timely software updates and cautious email habits are two of the most effective defenses available to any individual or organization.