Targeted ads are already a serious leak of information.
If somebody looks over my shoulder and sees the ads presented to me, they can infer things about me.
Also, if a malicious actor targets an ad to a group of people, and some of these people buy the advertised items, then the actor can infer things about those people not necessarily related to the items sold.
If somebody looks over my shoulder and sees the ads presented to me, they can infer things about me.
Also, if a malicious actor targets an ad to a group of people, and some of these people buy the advertised items, then the actor can infer things about those people not necessarily related to the items sold.