CryptoLocker is an especially insidious form of Ransomeware malware that was first detected in the wild in September 2013, restricts access to infected computers and requires victims to pay a ransom in order to regain full access.
What makes CryptoLocker so bad is the way it encrypts the user data on your hard drive using a strong encryption method. This makes it literally impossible to
Source: How to protect your computer from CryptoLocker ransomware malware ?