Recently I have been seeing this type of Malware on Macs much more often.  This is a great article describing how it can infect you.  I have said it before, and I will say it again, never update or install flash.  There is nothing on the web worth the risk.

This malware is not removed by simply running Malwarebytes.  Thats a good start but there are a number of other steps that need to be completed to get rid of it.  The article is a good place to help you to understand what you got from that flash installer.