I believe advertising based on tracking users across websites is more of a recent phenomenon. I don't really have a problem with a contextual ad based on what I

I believe advertising based on tracking users across websites is more of a recent phenomenon. I don't really have a problem with a contextual ad based on what I'm currently looking at. I have a problem with ads that are contextual based on everything I've been visiting for the past month. I doubt the effectiveness of the ad is drastically improved in the second case. But even if it's improved only by 10%, the ad industry would rather aggressively violate users' privacy to get that extra 10%.