I get the message "Install Adobe Flash" can't be opened because it was not downloaded from the Mac App Store. This is the first time I have gotten the message. What do I need to do?
What is your operating system & version?
you'll need to edit the security settings to install programs 'Mac App Store and identified developers'
Open the Systems Preference and go to Security & Privacy. There will be a section in the 'General' tab for 'Allow apps downloaded from:" The default selection is 'Mac App Store'. Change this setting to 'Mac App Store and identified developers".
This screenshot is taken on OS X 10.10 (Yosemite), so it may look slightly different if you're on a different OS X version.