I'm trying to program an app for Android that is capable of running in the background and opening pop-up windows from time to time over the main app that the user is using. Is this possible? Do you think an antivirus could block it?
(I haven't tried anything, just a friend suggested that maybe a mobile antivirus could block it)
Security apps (which might be part of the OS on the device) can potentially identify and block harmful behaviour, so it's definitely possible that an app creating popup windows over other apps would be blocked. Normal apps aren't supposed to be able to do that, for obvious reasons, and using features like Accessibility Services for non-accessibility purposes can be considered an abuse of those features (Google requires you to fill out a form declaring exactly what you're using it for) and could be blocked by a security app by default.
The best thing you can do is test it on a range of devices, with a range of these "security" apps, and see what they restrict and if they allow the user to whitelist apps. That way, if they genuinely want your app's functionality, you can give them advice about how to get it working on their device.
If you want something that "just works", then you should use the standard tools available to apps, like notifications and toasts. Anything non-standard (and especially with behaviour similar to malware) is more likely to run into problems given the wide range of environments an Android app can be running in, and how more restrictions are being imposed on apps with every update.
