Google announced new "safeguards" to "protect the quality of our ad network, and the benefits to our publishers and the advertising ecosystem," they said. This includes the site verification process and Google is enhancing its defenses even more by improving the systems that identify potentially invalid traffic or high risk activities before ads are served.
It isn't 100% clear what is changing but Google did say there is a chance this can impact your earnings as an AdSense publisher. Google said "While most publishers will not notice any changes to their ad traffic, we are working on improving the experience for those that may be impacted, by providing more transparency around these actions. Publishers on AdSense and AdMob that are affected will soon be notified of these ad traffic restrictions directly in their Policy Center."
I wonder if any of you received notifications yet?
Forum discussion at Twitter.