My computer showed an "update available" message for Flash, and I attempted to download it to a MacBook Air. The Mac did not want to download if not from "App Store," so I had to bypass normal security. Then the download did not perform well, and it tried to complete install before I finished checking that I had read terms and such. Worst of all, when I quit the install, I was taken to a not very pretty, not very Adobe-like thank you page.
Has anyone else run into this? Did I download a program that might have trojan files? Do I need to uninstall it, and if so, how?
Flash Player is not posted to Apple App Store, therefore will not download from there. Flash Player is available for download at https://get.adobe.com/flashplayer. The URL from the official Adobe Flash Player update notification is slightly different, but still adobe.com.
From your post, it's difficult at best to determine what you downloaded and from what website it was downloaded from. If you still have the file you downloaded, you can right-click on it and select Get Info. When the file Info dialog window opens, look in the More Info section (you may need to expand it) for the download URL. If the Where from URL starts with https://get.adobe.com/flashplayer then it's official Flash Player.