I don't think they do (yet), but having an option that allows it is probably the sensible move... Netflix, who've famously been successful with this crackdown,

I don't think they do (yet), but having an option that allows it is probably the sensible move... Netflix, who've famously been successful with this crackdown, do. Have add-on accounts and you extract a little more from people who were doing small-scale sharing with one or two others, and make it less likely that they'll cancel.