Searching for virus in apps - why?

If I get infected with a virus while surfing the internet, is it likely that that virus will hide in an allready installed app in my android phone? To me it seems unlikely. My apps are allready screened when they were installed, and I don’t think viruses will go and hide in an app - so WHY does all(?) anti-virus apps start their screenings with the installed apps?? Shouldn’t they start with the most likely places a virus would hide?

Hi, I can recommend you reading this article:
https://blog.avast.com/what-android-users-need-to-know-about-malicious-apps

Also, apps are not our only scope, there are more security elements in our app - the Web Shield, File Shield, App Locking, Privacy Advisor and many others. See the app’s Settings > Protection.