The Life of an Ad Interest

The Yahoo! Privacy team sometimes receives the question of how long we retain a web browser’s ad interests. The answer is a bit complicated but I’d like to take a moment to review the life of an ad interest and how for the most part that life is a fairly short one – typically less than a few weeks.

Before an ad interest can be determined, a category must first be created. Yahoo! has nearly 400 standard interest categories in the US (these can viewed from Ad Interest Manager). Categories fall across a range of topics such as iPods, Ford Trucks, Kitchen Remodeling or European Travel interests. Once a category is created, the next step is scoring interest in that category.

The birth of an ad interest begins when an interest scoring rule is triggered in our backend ad interest systems. Only a few key events are reviewed for scoring today: searches, page view, ad views, and ad clicks. Note – our new mail system processes email keywords similarly to “searches”. These events are funneled to a special set of servers at Yahoo! which score each event for interest in a category. Each category may give different scores to different events. For example, for an interest in Gifting Flowers the system will typically weight a search higher than a page view, whereas the Truck interest category may score a visit to the Yahoo! Autos site higher than a generic “truck” search. The resulting event score is then added to the existing score for an ad interest in relationship to an anonymous browser cookie.

Once an event has been scored for an ad interest it is held in these systems for a short period of time just in case something fails and data needs to be reprocessed. After a few days the raw event information is purged from these systems and only the resulting scores remain. It’s important to note that when a user opts-out of receiving interest-based ads, their activity is no longer sent to our backend ad interest systems for scoring (this includes from the new Yahoo! Mail platform) AND ads are no longer selected for that user based on interests.

Now that we have a score for an ad interest, the question of its life span can be addressed. Ad interest scores at Yahoo! “decay” – meaning that each day that goes by, each ad interest category will slowly reduce its score for a browser cookie. Each ad interest category has a different decay rate – tied to how long it typically takes to make a purchase decision. For example, an interest in Gifting Flowers may live a very short period of time – less than a week. Whereas an interest in Trucks lasts longer. While most ad interest categories will decay out scores within a few weeks, the maximum decay is about 90 days.

Interest scoring and decaying are always occurring at the same time. On some days activities may increase the score in a particular ad interest category while other interests are decaying because no activity occurs in relationship to them. If a browser cookie event isn’t processed through our backend systems for 90 days, all ad interests for that browser cookie will decay out.

That’s it! In quick review, the steps are: ad interest category creation, select event scoring, raw data purging, and category interest decay.

To learn more about other forms of log data retention at Yahoo!, please read this blog article.

To learn more about interest based advertising at Yahoo!, view what we believe your ad interests are, and see other general ad interest related information, please visit .

Shane Wiley
VP, Privacy & Data Governance

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