What is malware?

Malware (malicious software) is any software intentionally designed to cause harm to systems, steal data, or gain unauthorized access. Types: Virus: attaches to legitimate files and spreads when the file is executed. Worm: self-replicating, spreads across networks without user action. Trojan: disguises itself as legitimate software. Ransomware: encrypts victim's files and demands payment for the decryption key (WannaCry, REvil). Spyware: secretly monitors user activity and exfiltrates data. Adware: displays unwanted ads, often bundled with free software. Rootkit: hides its presence by modifying the OS. Keylogger: records keystrokes (captures passwords). Botnet: network of compromised machines used for DDoS or spam. Defense: antivirus/EDR, keeping software patched, not running untrusted code, email filtering, application whitelisting, and user training.