It's an instance of the general "social network" problem of privacy. If you are in a group of friends who all like some particular artist, you are very likely t

It's an instance of the general "social network" problem of privacy. If you are in a group of friends who all like some particular artist, you are very likely to like the artist too. It doesn't mean you'll always like them, but there is a strong correlation. This can be done for so many characteristics, educated or not, gay or straight, liberal or conservative. Now, if a sizeable portion of your group is in some social network where they share details of their life, like, say facebook, then facebook will a) know you exist because your e-mail address and your phone number will be uploaded to them as part of the address book upload that apps have and b) know all these things about you without you ever telling facebook, having joined facebook, or being able to do anything about it. As you observed so well, the same holds true for genetic testing. Maybe some point in the future you'll receive spam mails for preventative health measures concerning some genetic disorder that runs in your family. Or you'll have a hard time getting life insurance. I don't want to live in such a world, but it's coming.