Talos reverse engineered CryptoWall 4 to better understand its execution, behavior, deltas from previous versions. Talos has devoted a significant amount of time to better understanding how ransomware operates, its relation to other malware, and its economic impact. This research has proven valuable for Talos and led the development of better detection methods within the products we support along with the disruption of adversarial operations. Despite global efforts to detect and disrupt the distribution of CryptoWall, adversaries have continued to innovate and evolve their craft.”]
Source: https://blog.talosintelligence.com/2016/05/cryptolocker-4-white-paper-available.html