Well, one brief thought is that groups concerned about potential infiltration tend to adopt a decentralized structure - kind of like a collection of "cells" rather than a centralized organization. That way, if one cell gets compromised, it doesn't necessarily mean all other groups are compromised, as well. Communication is indeed worth thinking about, since it is well known now that most electronic forms of communication (email, cell phones, social media) are at least partially monitored. Widespread video cameras allow vehicle and possibly individual movement to be monitored. Yes, a challenge for sure...