Its not strictly "illegal" to advertise in law terms just unwelcomed and usually gets you banned from certain channels, networks for doing so.
One of the most common methods of "innocently" (although annoyingly) advertising as i'm sure you might notice on these forums is by placing a "signature" with your name/channels/network in it after your posts, or by filling in the profile (which asks for channels list).
However the idea is that your suppose to ask your friends to join your network/channel, and they ask theirs and so on and so forth.
Eamonn.
