Adwords has a bug that let advertisers to impress their ads for free. This bug relates only to HTML5 banners.
If CTA button is placed outside the banner and the banner is downloaded up to Adwords in zip file, a visitor can not click such CTA button in the banner. And an advertiser can set very high price for such ads, so that banner can take millions of impressions a day across the world. And the advertiser will not pay for these impressions because the CTA button is outside the banner. No clicks, no payments for impressions.
So advertisers can promote theirs brands. Or an advertiser can place his phone number, and a user can call him without
clicking ads. So advertisers can get their clients, but Google and publishers will get nothing.
And Google knows about this problem but does nothing, maybe it does not consider it as a problem (as it was in the official responce from Google).
It's seems that this problem till now mainly has affected Russia and Ukraine but it is expanding to the other countries of the world. But CTR dropped significantly (as users click much less) and the revenues dropped as well. And the webmasters have nothing to do except spending a lot of time to block such ads in Adsense account.