Ransomware is a serious threat to your data, and you need to take steps to protect yourself. If infected your data is encrypted, and then a ransom note appears on your computer asking for a ransom of $500 or more to get your data back. So please back up your data.
Measures to protect yourself include not running as an administrator in Windows, not clicking on links in emails, and being suspicious or anything trying to install on your computer that you didn’t ask for. Also download apps only from known good sounces, use a good SPI-class firewall, and run a top-rated antivirus. Perhaps must important is to run a cloud backup service such as Carbonite, CrashPlan, or Backblaze. These cloud backup apps are secure, and help keep your backed up data secure from ransomware.
Becoming more and more common in Windows, now we’ve seen the first ransomsomware for MacOS. It’s embedded in a torrent client and called Transmission. I don’t recommend using torrent software at all. Read more about this serious threat here: http://www.macrumors.com/2016/03/06/mac-ransomware-transmission/