In the last four months of 2013 alone, the malicious software raked in some $5 million. In 2007, a strain of bad app called GPCode, or Sinowal, encrypted files on the machines infected with the infected machines. The only way for a keyboard jockey to regain use of the files is to pay a ransom for a digital key to decrypt the data. The bad app is the result of an evolutionary process that can be traced back to the rogue anti-virus campaigns during the 2000s.”]
Source: https://www.csoonline.com/article/2134440/cryptolocker-s-success-will-fuel-future-copycats.html