Cryptolocker is a nasty piece of malware that encrypts the files on your computer and holds them ransom. If you don't pay for a code to unlock the files, you don't get them back. FireEye and Fox-IT recently launched a tool to help users get their files back.
If you haven't been infected yet, you should make sure you have the necessary precautions against malware like Cryptolocker:
Antivirus. We recently covered the best antivirus software and that's your best line of defense. No antivirus is foolproof, but it can go a long way. Over at FoolishIT, they've got Cyrptoprevent—a program designed specifically to block this type of attack.
Reliable, cloud-based backup. If you can't decrypt the files, the only way to get your data back is from a backup. In this case, your recovery options are better withan online backup service. Online backup services can restore your files to a time before they were encrypted, and Cryptolocker infects external hard drives so they won't help you here.
However, if you're already infected, Decryptolocker allows you to email them an encrypted file, after which they will send you a master decryption key and tool to free your files. The keys they are using are based on the original version of Cryptolocker, so they won't always be able to help with newer variants. If you can, you're better off restoring your files from a backup, but this is a good last line of defense.