Ransomware is a type of malicious software that encrypts files, making them inaccessible until a ransom is paid, usually in cryptocurrency. Ransom demands can range from a few hundred to several thousand dollars, causing significant disruptions and financial losses. Key examples of ransomware include WannaCry, Petya, CryptoLocker, Ryuk, REvil, and Snake. To protect against ransomware, it is crucial to keep software updated, use anti-virus solutions, be cautious with unknown attachments or links, and regularly back up important data. Effective protection tools include backup solutions, anti-virus software, firewalls, and ransomware-specific solutions. Free protection options include Windows Defender, Malwarebytes Anti-Ransomware, Bitdefender Anti-Ransomware, Avast Anti-Ransomware, and Kaspersky Anti-Ransomware Tool for Business. Ransomware can be categorized into locker ransomware, screen ransomware, and encrypting ransomware.