Google has warned webmasters many times about the dangers of using manipulative or deceptive behavior. Now Google has issued a special warning regarding a practice where a website inserts new pages into a user's browsing history.
While deceptive behavior has long been against Google's quality guidelines, for them to issue a special warning about manipulative or deceptive behavior, it means that likely they've seen a giant upswing in the number of users encountering this practice.
For example, when users click on a web page from the Google search results, but don't find what they were looking for on that page, normally they would click the back button and return to Google's search results. However, some users are instead being taken to a spoof search results page that is actually entirely advertisements, such as this:
This is something I have seen with a lot more frequency lately, and Google stance is that a website utilizing this practice could have manual action taken against it, including removal of the offending sites from the Google search index.