After a long and costly legal battle in the European Union, Google is making some changes to the way it serves ads to European users. Under a new European user consent policy published Monday, AdSense will require any site serving European users to require explicit consent before those users can be tracked. "You must use commercially reasonable efforts to disclose clearly, and obtain consent to, any data collection, sharing and usage" that results from a Google product, the new policy reads. It's a serious change from previous consent standards, which allowed for passive permissions that rendered tracking cookies effectively invisible.

"We recommend you start working on a policy-compliant user consent mechanism today," Google program manager Jason Woloz said in a post accompanying the new policy. Google's own AdSense blog already provides an example of how such a policy might work in practice, placing a banner at the top that informs visitors that tracking cookies are in place, and provides buttons through which users can accept or refuse the tracking.

It's unclear what immediate effect the new policy will have, but the long-term effects are likely to be profound for both Google and the web at large. The vast majority of Google's revenue comes from targeted advertising, so any significant reduction in the company's ability to collect data would strike directly at its revenue stream. At the same time, while the policy ostensibly only bears on webgoers based in the European Union, it's likely to change policies for nearly every site serving ads through Google, since nearly every site on the web serves visitors from the EU.