A new ransomware named Bad Rabbit is spreading mostly in Europe and Russia and is spreading to other countries, according to ZDNet.com. It infects websites and prompts users to install a fake Flash update. The ransomware will attempt to spread across networks once it is installed on one computer.
Windows Defender can remove this threat with update 126.96.36.199 and higher, so make certain that Windows Updates are current.
US-CERT (U.S. Computer Emergency Readiness Team) has logged the issue.