How to find the source of the banners on Android?

Today the phone suddenly began to show pop-UPS, advertising banners! On top of all Windows. You receive the banner and a few seconds disappears.

This is me, to put it mildly, surprised because:
1. The application set on the phone is old and limited. All from famous authors. No games or questionable SEOs-launcher.
2. In the last days NOTHING new was raised only this morning, Firefox updated. (And the banner appeared earlier today and already had 4 pieces).
3. In General, I'm a neat user dumps sharyus.
4. Put Dr Web Lite, he scanned the application and found nothing.

How to find the infection? Phone MotorolŠ° with a clean 6.0.1 Android, without rooting.

UPD Googled the article, as someone hacked into the Wi-Fi and prescribed left in the router DNS. Checked myself - no normal address. Besides, the computer does not have any anomalies (PAH-PAH). Version is not required.
July 8th 19 at 15:50
3 answers
July 8th 19 at 15:52
Solution
I think I found the cause.
This file Manager: https://play.google.com/store/apps/details?id=com....
I was mislead by the fact that I put it "on watch" for another 2 weeks ago, but then somehow got distracted and forgot. And today first launched, and he apparently intensified. And in my head I was sitting "well I anything new did not put."
Judging by the reviews, I'm not alone.
July 8th 19 at 15:54
When the banner appears press the button the recent apps. From the window, the banner will be the name of the application that it shows. He was so tortured. Was full-screen banner showed the alarm clock app in the free version.. So like a good alarm clock, I decided to buy the paid version and the banner disappeared. Would not like - would remove the app just.
There is nothing in this list. Especially all powerreal and waited. Wait. - Evie commented on July 8th 19 at 15:57
July 8th 19 at 15:56
You are sure that Dr.Web found nothing? As in the last version that you specify, the app contains Adware.Patacore.1, which is quite a long time attached to the base.
You wouldn't have in this case log files and the application itself?
Well, he wrote that he found the threats - 0.
But is this true - how do I know...
I put the application approximately 2-3 weeks ago.
Dr Web already removed, so maybe no logs (or they are somewhere left to lie?)
But banners from that moment never came. - Evie commented on July 8th 19 at 15:59
: I just checked what the latest version of this application, and it issued its entry was on a well-known adware, here and was surprised that nothing was found.

No, when you uninstall the application all the logs are also deleted. - Evie commented on July 8th 19 at 16:02

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