Ransomware has emerged as one of the biggest threats to internet users in recent times. Cryptowall 4.0 ransomware has been spotted to be delivered as part of a Nuclear Exploit Kit. The cyber gang, dubbed the “BizCN gate actor” began distributing the ransomware in payloads from the exploit kit as early as November 20. There is not much you can do, as the encryption it uses is very strong and almost unbreakable. The only options you are left with are: Format your computer and restore your data from the backup.
Source: https://thehackernews.com/2015/11/cryptowall-ransomware-malware.html