Malicious software designed to damage, exploit, or gain unauthorized access to computer systems, a major internet security threat. Malware evolved from early computer viruses spreading via floppy disks to sophisticated internet-distributed threats including viruses, worms, trojans, ransomware, spyware, and keyloggers. Notable examples like ILOVEYOU (2000), Stuxnet (2010), and WannaCry (2017) caused billions in damages. Malware distribution methods exploit email attachments, software vulnerabilities, malicious websites, and social engineering. The malware ecosystem includes criminal marketplaces selling exploit kits and ransomware-as-a-service. Combating malware requires antivirus software, security updates, and user awareness. Malware's evolution reflects the internet's central position in society and the lucrative opportunities for cybercrime, making security an endless arms race.