Google’s John Mueller and Google’s Gary Illyes both confirmed that Google started to roll out the penalty for mobile websites that use intrusive interstitials.
What are intrusive interstitials?
Google does not like the following interstitial types:
Websites that display a standalone interstitial that the website visitor has to dismiss before seeing the actual page.
Website layouts where the directly visible (“above-the-fold”) content looks like a standalone interstitial, with the original content below the fold.
Websites that show ads that cover the main content. This applies to ads that are shown immediately when the visitor comes to the page, and ads that are shown when the visitor scrolls through the content.
Which websites are affected?
This new penalty only applies if a searcher clicks from Google’s mobile search results to a website that then displays one of the interstitials mentioned above.
The new penalty does not impact desktop searches. It seems that some websites lost 10 positions after the release of the new penalty. Some examples can be found here.
It’s better to avoid spammy techniques. They might deliver short-term results but they will hurt your website in the long run. Better focus on optimization techniques that are good for your website, good for your visitors, and good for search engines.