Security experts at Bitdefender have discovered a new spam campaign that targeted a few hundred users. Bad actors sent email messages containing a bogus Incoming Fax Report that carried a help file with the.chm (compiled HTML) extension. When victims opened the file, they were presented with a help window, meanwhile a strain of malware downloaded the popular CryptoWall ransomware and executed it. Ransomware is a specific family of malware that lock victims files and requests the payment of a fee to unlock them.”]
Source: http://securityaffairs.co/wordpress/34646/cyber-crime/help-file-serve-cryptowall.html