Cryptowall 2.0 is a trojan that encrypts your files and holds them for ransom, meaning that you will have to pay money in order to get your files back. There is no other sure way to decrypt your files, so the best thing that you can do is try to protect yourself from Cryptowall infection. Backup your important data so that you can recover it if infected, keep your anti-virus software up to date, and deny programs the ability to run in your Application Data folders. You may also want to block Flash ads since that is one method that the trojan uses to infect computers. More information about this trojan and how to protect yourself from it can be found at http://grandadmiralgamez.blogspot.com/2014/10/how-to-prevent-being-hit-by-cryptowall.html.