Comment by mrsaint

It used to be IRC mainly. Efnet, later Linknet or similar. Often involved the group maintaining their own server linked to the network (preferably hosted by an admin of a big university). The server not only made sure that only encrypted connections were allowed (hi Blowfish), but also that clients authorized to use it automatically received a spoofed IP/hostname (something childish like @i.am.too.leet.for.paradox.org) to hide ones true location.