When browsing the web, be very careful of messages such as the one above. It is disguised as an update to Flash Player, but it is not genuine. What it actually wants to do is install other software on your computer.
It warns that ‘Your system is at risk!’, but Adobe don’t tend to use exclamation marks in their installations.
The Adobe Flash logo is correct, but there is no option to cancel the installation – the buttons are for ‘update’ or ‘install’. Also, at the bottom of the window, it says ‘preparevideo.plugin-search2update.com’.
These are all clues that it is not a genuine update from Adobe. If you want to install Flash, make sure you do so directly from the Adobe website: https://get.adobe.com/flashplayer/otherversions/, or to update a previous installation, go to System Preferences – Flash Player.