reddit

“The changes involve both Doubleclick -- an online ad company Google bought for just over $3 billion last year
-- and Google's own Adsense system. They work in different ways: Doubleclick tracks the browsing history of a user and builds up a picture of their interests, while Adsense ads are specific to a particular website's content (though they do take
into account a user's geographical location to provide relevant ads).” source...