CryptoLocker is a type of malicious software known as ransomware. It infects a computer and encrypts the user's files, making them inaccessible. The attacker then demands a ransom, usually in Bitcoin, to provide a decryption key that will unlock the files. This malware typically spreads through email attachments or malicious downloads. Once activated, CryptoLocker displays a message instructing the victim on how to pay the ransom. If the payment is not made within a specified time, the files may be permanently lost, highlighting the importance of regular data backups and cybersecurity measures.