The STOP Ransomware has been the most actively distributed ransomware in the wild for the past year. It targets consumers through cracked software, adware bundles, and shady sites. In order to distribute STOP, the ransomware developers have teamed up with shady sites and adware bundles that install the malware. The $490 ransom, which doubles after 72 hours to $980, is the most common variant of the ransomware. There are more than 159 variants that we know about, with the ransomware pumping out 3-4 variants a day.
Source: https://www.bleepingcomputer.com/news/security/meet-stop-ransomware-the-most-active-ransomware-nobody-talks-about/