Apple announced that it will block out-of-date versions of Flash Player after a major update to the Adobe software two weeks ago. Apple last night updated its blacklist to include older versions of the software. The move is not an unprecedented move from Apple, which on several occasions dating back to 2012 has proactively blocked Flash. Windows and Mac OS X users were urged to update to Flash Player 17.0.188.188188. None of the security flaws have been publicly exploited, but all of the vulnerabilities enable an attacker to remotely take control of a compromised computer.
Source: https://threatpost.com/apple-blocks-outdated-flash-player-versions-in-os-x-safari/113038/