CryptoLocker is a Ransomware program that was released around the beginning of September 2013 that targets all versions of Windows including Windows XP, Windows Vista, Windows 7, and Windows 8. This Ransomware will encrypt certain files using a mixture of RSA & AES encryption. When it has finished encrypting your files, it will display a CryptoLocker payment program that prompts you to send a ransom of either $100 or $300 in order to decrypt the files.
Read more here – http://www.bleepingcomputer.com/virus-removal/cryptolocker-ransomware-information