What worked for me is this:
(1) Download the flash installer
(2) Locate the installer (it's a dmg file) and double-click to mount the image
(3) When the image mounts on the desktop, DO NOT DOUBLE CLICK THE INSTALLER. Instead, control-click on the installer and select "Show Package Contents"
(4) A Finder window will pop up, with a folder called "Contents" inside. Open the "Contents" folder.
(5) Inside "Contents", there is a folder called "MacOS". Open it.
(6) Inside is a Unix executable file caled "Adobe Flash Player Install Manager". DOuble-click to un.
(7). It will open up the Terminal first, but then it will look like a regular install/update.
Hope this helps,
C