Prevent unauthorized use of an outside user

[kh99]

As you said, doing it by ip isn't perfect, but I don't know how else you'd do it. I remember a while back someone had an idea to allow 2 ip addresses per user, but you'd need a mod to do that and I'm not sure if it ever got past the idea stage. Anyway, even doing that, I'm sure there'd always be someone who needed another one for some legitimate reason.