Something to think about

[Danimal]

Deleted

[Great-Kazoo]

Know by their Tattoo's

[Singlestack]

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...

[Omicron]

*Ponder*

[Inconel710]

The first rule of Fight Club is YOU DO NOT TALK ABOUT FIGHT CLUB!

[SideShow Bob]

Remember folks, Big Brother is listening/watching. Private face to face discussions and planning is the only way to maintain security.

[Tinelement]

Mouse traps under their beds.....

[rbeau30]

1)
With a good Cipher. However you must know the capabilities of the adversary you are protecting your information from.

Consider reading: The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography ISBN-10: 0385495323

It sounds like it is a hard read, but it is actually well written and I learned a lot, and helped me in my job.

2)
Consider a combination of different cells that could be cut off easily if problems arise. Also a good vetting program involving trustworthy persons, with concrete and non-negotiable requirements for joining.

[Wulf202]

I read that at first as "with a good chipper..."

[Great-Kazoo]

1)
With a good Cipher. However you must know the capabilities of the adversary you are protecting your information from.

Consider reading: The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography ISBN-10: 0385495323

It sounds like it is a hard read, but it is actually well written and I learned a lot, and helped me in my job.

2)
Consider a combination of different cells that could be cut off easily if problems arise. Also a good vetting program involving trustworthy persons, with concrete and non-negotiable requirements for joining.

This leaves me out.