Google most important privacy policy changes happen almost two years ago. The change was announced as a clarification of the policies which will mainly be used to simplify and improve services. Now that the changes are effective, it is interesting to observe what the consequences of the new policy are and what has changed. In this blog post I focus on Google tracking capabilities and show that the changes allow Google to improve significantly the way it tracks users on the web.

The claim about DoubleClick cookie information

One of the few protective claims Google made in its policy was that “[they] will not combine DoubleClick cookie information with personally identifiable information unless we have your opt-in consent”. Some understood that Google would not combine information from the Google Account with information from DoubleClick ad-network, but that was not the case.

Using information from the Google profile

As a matter of fact, Google has so far combined many pieces of information from its ad network with information obtained from Google profiles. Your age and gender have already been shared with DoubleClick advertisers for many months now as shown on Google Ads Setting page. At the beginning, these data were shared on an opt-in basis through the “+1 personalization page”. It was not obvious that his page controlled how information from your profile was shared with advertiser as this was only mentioned as “+1 and other profile information”.

This page shows part of the information advertisers can use to target you.

The “+1 personalization” (see below) page has been removed when Google announced “ad endorsement” and now the URL of the page redirects to the ad-endorsement page. As a matter of fact, it is no longer possible to opt out of ads on the web be based on your Google profile without opting out of all interest based ads.

This page was buried in Google+ settings and was removed when Shared Endorsement was announced.

This change came with no announcement, because the privacy policy only prevents Google from combining PII from the Google profile.

Ad customization based on visited website

The policy does not prevent Google from associating your visits on websites affiliated to DoubleClick to target your Google profile. As a matter of fact, your Google account can be retargeted by DoubleClick affiliated websites you visited. This feature — called Remarketing list for search ads – lets advertisers retarget previous visitors on Google Search.

Technically, Google cannot recognize when a user visited a site web affiliated to DoubleClick because the domains associated to the cookies are different. When you’re doing a search on Google, Google reads only cookies attached to “” domain, whereas on Google Display Network (i.e. the set of websites with DoubleClick ads) cookies are attached to the domain. Google knows the DoubleClick cookie ID of people who visited a website on Google Content Network but it does not know their Google ID. This is problematic because when you do a search on Google, you do not reveal you DoubleClick ID but just your Google ID. So when you do a search, Google cannot know if you’ve visited a website which does retargeting.

To solve this, Google redirects your browser from the domain to the domain. When you visit a website which wants to retarget you, DoubleClick redirects you to domain and Google adds your Google ID to the list of persons who visited the advertiser’s website. Next time you’ll do a search Google will recognize your Google ID and retarget you with ads for the website you visited. The figure bellow explains how Google records that a user visited the website ABC (you can capture the actual frames on

Through this process, Google associates the list of websites affiliated to Google Display Network (it means with a DoubleClick tag) you visited to your Google ID. Consequently, part your web browsing history (the part containing websites which do remarketing) is actually combined to your Google profile and you cannot review it. Notice that Google never proposed a way to know which website you visited and try to retarget you, but while Google could have claimed that your browsing history was only associated to you “anonymous” DoubleClick ID, it is now attached to your personal Google account.

Summary of what Google can combine with DoubleClick

To summarize, Google cannot combine personally identifying information from your Google account with you DoubleClick cookie information, yet it can:

– Use information from your Google account (age, gender and probably very soon a list of your interests) to personalize ads that you see on DoubleClick affiliated website
– Link visits on DoubleClick affiliated websites to your Google profile and retarget you when you do a search on Google.

In the end, Google privacy policy with regard to advertising is well summarized on this page:

  • “[They] don’t share personally identifiable information with advertisers.
  • [They] don’t allow advertisers to show ads based on sensitive information, such as those based on race, religion, sexual orientation, health or sensitive financial categories.”

In the next page, I consider how Google combines information from Google profile and DoubleClick with data obtained though Google Analytics.