For a moment I thought a friend of mine had become a Mormon. There in my news feed on Facebook, between posts from people I barely know and photos of babies (I'm 30), was a status update that read: "No matter how bad your past has been, you can change and move on." How nice! But the post wasn't by or even endorsed by anyone I know: it was an advert for the Mormon Church placed in my feed (where I don't remember ever seeing advertising) as part of an online mission of such scale it would be the envy of its most prominent believer's presidential campaign.