Security researchers of the Cyber Threat Alliance have conducted an investigation into the cybercriminal operations leveraging CryptoWall 3.0 ransomware. The most recent variant of the CryptoWall ransomware emerged in-the-wild beginning in January 2015. This ransom is usually paid in Bitcoin, with a (sometimes empty) promise of providing a decryption utility in order to recover all affected files, as a result of a successful, cleared ransom payment. Over 400,000 infection attempts have been logged across 49 campaigns, with over 4,000 samples of the malware.”]
Source: http://securityaffairs.co/wordpress/41642/cyber-crime/cryptowall-3-0-325-million.html