To even talk about this out in the open is a major mistake, though to find ideas of how to communicate secretly with someone in this day and age is a divine challenge. -Private forums: apparently safe from the average bozo looking at what you are discussing, yet less safe when taking into consideration the owners of your webspace that have direct access, and robots that can find a password in a blink. Making the password extremely complicated would keep the robot or program busy for a few days but it WOULD find it.
(advice to all forum owners, don't use the same password for everything you need a password for. You may force malicious beings to take advantage of your laziness and "hack" your fortress)
I am avoiding the other known fact that compromises what is written in forums of robots sweeping the net for information then sold to governments and secret services, or programs' databases (like msn) poured into various research branches (homeland security, FBI, interpol). Radio waves are also sucked in and analyzed. Difficult to know if there still is a media free of operator pluggin you through while listening to your private phone call.
-ventrilo/teamskpeak/skype: how safe are these programs? Are they filtered and watched by owners and those who own them? The phone isn't safe, as we know, but is it the same too for the former three?
-letters: not as slow as when a messenger would be sent running across the land to deliver a message, but still not so immediate as the first two "unsafe" modern means of communication. Are letters scanned, confidential?
-The SUB-net: who knows how to use this? Does info there actually stick out more than above the surface?
Code language: this can be applied to all four above. A code can be cracked, and people are trained to do just that. Codes do however serve their purpose in shutting the enemy's lights off. And by the time the code is cracked, a new code is applied.
Making a program that only special users of a group would be given could translate the coded text.
Meeting people! Meet you in the park at noon. Exchange info with low voices away from electronic devices. This is when members, like before, have to trusted.
All this to send each other results of last clan war, or samp gossip? I doubt that