OP: I'm a network administrator and someone showed me this and I don't understand how it works.. how do I prevent people from doing this sort of thing on my network? Pretty sure this is on the same lines as WifiKill if I'm correct? The device use arp and pretends to be the router?
I've been struggling with this issue for a while myself. By no means am I a network admin but when working with my old high school for a few months I discovered all the kids with laptops were running Cain to get a few odd bits of data sent their way. Never figured out how to stop it.