Well, first of all, they're a provider running IIS and, I'd guess, a much bigger winblowz network... so they're probably frightening that someone on their backbone would actually be posting a "what to hack" sort of database or whatever -- kind of like they took it personally.

Second, here's their AUP. While "hacking" or security sites aren't expressly against their AUP, it would appear they've left themselves prety wide open to "at its sole discretion, remove them from the network."

You have to think, though... if someone's been at an ISP for a given length of time and has kept up their end of the bargain - removing them from the network has to be pretty tough... I mean, wouldn't you normally try to contact someone, first, before just yanking their connection on them? I mean, chances are, you've pretty much lost a customer the second you turn off their IP feed... you'd have to be pretty convinced - and, in my experience, that's not generally something that's done lightly, particularly for continuing customers.