The ad space is data. If you chose the right categories you can reasonably identify someone. The whole purpose of behavioral advertising is to identify groups,

The ad space is data. If you chose the right categories you can reasonably identify someone. The whole purpose of behavioral advertising is to identify groups, you can make those groups =1 if your clever. Look up deanonymization. It's one of those problems that also affect researchers because it's hard to keep db data anonymous too.