Screen with warning of Virus and malicious applications pop up screen
MacBook, iOS 10.3.3
Started when I got notice to update Flash player.
That wasn't Flash. You installed a newer forum of malicious adware that intentionally blocks access to certain sites. All in the attempt to prevent you from removing it and believing you need to call whatever crook's phone number is displayed.
In the future, never, ever believe any site that tells you to update Flash, Java, that you need a codec, or anything else that comes from them. The one and only place to acquire Flash is from Adobe. Java from Oracle (for the latest version), or Java 6 from Apple.
Restart the Mac in Safe Mode (restart and hold down the Shift key). This will prevent all but the most basic OS functions from loading. From there, you'll be able to download and run MalwareBytes for Mac. It will look for, and offer to remove any garbage it finds.
The screen may flicker or draw with strange looking horizontal strips as Safe Mode boots. That's normal since the OS is using a very generic video driver instead of the one meant for your graphics hardware.
I have this also they also are using the AppleCare logo
DO NOT select <CLOSE> It in some cases downloads unlimited files. Close tab.
Screen with warning of Virus and malicious applications pop up screen