It isn't new, and people have been joking about finger smears since this kind of unlock mechanism came out (I remember making this discovery myself and promptly

It isn't new, and people have been joking about finger smears since this kind of unlock mechanism came out (I remember making this discovery myself and promptly switching my phone back to using a number pad). But it is worse than shoulder-surfing; you can just steal a phone, say, from someone's purse or off a table when no one is looking, and then unlock it. You don't have to stock the person, see them unlock the phone, and then steal it.