From: Apple Product Security
Reply to list

APPLE-SA-2015-10-20-1 OS X: Flash Player plug-in blocked

Due to security issues in older versions, Apple has updated the
web plug-in blocking mechanism to disable all versions prior to
Flash Player 19.0.0.226 and 18.0.0.255.

Information on blocked web plug-ins will be posted to:
http://support. [...]