Talos reverse engineered CryptoWall 4 to better understand its execution, behavior, deltas from previous versions and share our research and findings with the community. Ransomware is designed to hold users’ files (such as photos, documents, and music) for ransom by encrypting their contents and demanding the user pay a fee to decrypt their files. Despite global efforts to detect and disrupt the distribution of CryptoWall, adversaries have continued to innovate and evolve their craft, leading to the release of CryptWall 4.”]
Source: https://blog.talosintelligence.com/2015/12/cryptowall-4.html