Ransomware is a type of malware that infects a computer and restricts access until a ransom is paid. In 1989, the first ransomware, called the "AIDS Trojan", was distributed at an AIDS conference on floppy disks and encrypted files, demanding $189 to unlock them. Ransomware can enter systems through phishing emails, malicious attachments or files, or visiting infected websites. It aims to create fear and trick users into paying ransoms, but paying does not guarantee files will be recovered or that systems are malware-free. Daily data backups and using security tools like antivirus software can help prevent ransomware infections.