When users click on many mobile websites, they see a big interstitial pop-up ad prompting them to download the app instead. Google has announced that it will begin moving sites with these pop-ups lower in its search rankings.
Not all interstitials will be penalized, just those that hide "a significant amount of content on the transition from the search result page." And the change doesn't take effect until November 1. Still, concerned Web developers should begin making changes if they want to retain their high web rankings. The change will also be of concern to the mobile development industry, which could see fewer app installs as a result.
Of course, the irony in this announcement is that some Google sites use exactly this strategy to get people to download their mobile apps.