How to find the source of banners on Android?

Question

Android

Today the phone suddenly began to show pop-up advertising banners! Above all windows. A banner appears and disappears after a few seconds.
This surprised me, to put it mildly, because:
1. The set of applications on the phone is old and limited. All from renowned authors. No games or dubious launcher optimizers.
2. In recent days, NOTHING new has been installed, only Firefox has been updated this morning. (And the banners appeared just this afternoon and there were already 4 pieces).
3. In general, I'm a neat user, I don't rummage through the trash heaps.
4. Put Dr Web Lite, he scanned the applications - and found nothing.
How to find an infection? Motorola phone with pure Android 6.0.1, no root.
UPD Googled an article about how a person was hacked into Wi-Fi and registered the left DNS in the router. I checked with myself - no, normal addresses. In addition, there are no anomalies on the computer (pah-pah). The version is gone.

Answer 1

Seems to have found the reason.
Here is this file manager: https://play.google.com/store/apps/details?id=com....
I was confused by the fact that I put it "to watch" 2 weeks ago, but then how got distracted and forgot. And today I launched it for the first time, and it, apparently, became more active. And in my head I was sitting "I did not put anything new."
Judging by the reviews, I'm not alone.

Answer 2

When the banner appears, press the recent apps button. The window with the banner will have the name of the application that shows it. I suffered so much myself. It turned out that the full-screen banner showed the alarm clock application in the free version .. Since the alarm clock is good, I decided to buy the paid version and the banner disappeared. If I didn't like it, I would just delete the app.

Answer 3

Are you sure Dr.Web didn't find anything? Since the latest version of the application you specified contains Adware.Patacore.1, which has been added to the databases for a long time.
In this case, you did not save the logs and the application itself?