In the past 24 hours, Apple has released an update to the XProtect malware definitions. If your Macs have received the latest XProtect definitions, Adobe Flash Player will be blocked unless it is the version current as of yesterday (11.5.502.149).
If you have already updated your clients to that version of the Flash Player, good for you!
If you don’t want to be surprised by this sort of thing and have to scramble to address it, might I point you here?
Managing OS X 