COINTEL FOR BEGINNERS
Step 1: Compartmentalization.
Step 2: Isolation.
Step 3: Reduction.
Step 4: Repetition.
Step 5: Deduction.
After finding your leak, you have a few ways to approach this.
Scenario A.) You suspect you have only one infiltrator.
1.) Compartmentalize around them. Put them into a group you trust to watch them, give them nothing of value, allow them to stay to keep from having to deal with more infiltrators.
Scenario B.) You suspect you have multiple infiltrators.
1.) Same as A.1, save that you inform your most trusted people (the ones you've known the longest, the ones that are least likely to be traitors such as blood relatives) of what's going on and then REPEAT COINTEL STEPS TO ROOT OUR FURTHER TRAITORS.
A.2) Kick out the traitor. Warning, the feds will probably send in a new traitor. Screen all new applicants thoroughly.
B.2) You suspect the feds likely already have other traitors who are smart enough to spot COINTEL ops used against them in your group and don't want them there. Disband the group. Wait. Reform the group with your inner circle of most trusted people–relatives, lifelong friends, etc. These people are only allowed to invite their own relatives and lifelong friends, and so on. Do not allow random people to join.
So, suppose you manage to secure your group against infiltrators but the feds really, really want to know what's going on in there. How do you prevent this?
A few basic rules:
Every wireless phone, from smartphones to 'dumb' phones, to burner phones, can be tracked, intercepted, or have call and text records extracted or subpoenaed by LEOs. There are backdoor programs that will allow LEOs to turn on the mic and camera remotely and record everything nearby. Never take your phone to your meetings. Leave it at home. Screen for phones at the door and if anyone brought one, everyone is to leave for the day.
In the first case, you're relying on having a building that's completely cleared out of everything but the most basic of the basics–lights and heating/cooling, maybe not even those. This place should be completely bare, with nowhere for anyone to hide electronic snooping devices such as cameras and mics. If you're careful, and consistent about checking for bugs, you'll likely be safe.
In the second case, you're relying on the 'open field' tactic. A pasture, an old fire road at a random mile marker, an old fire station in the middle of nowhere on some backroad no one ever travels, but somewhere away from people. Bring a large tent if it's going to rain. Park all vehicles close to the meeting place, open doors, turn on radios to play loudly–or bring a battery powered radio or two for the same purpose, that is, fucking up anyone trying to use parabolic or laser audio snooping.
Never mention specific places, times, people, or plans out loud. Use notepads and burn the notes after if you have to. Never mention aloud a desire or plan to commit violence.
No tattoos, no hand signs, nothing. You will know your members, their immediate family, their wife/husband, and their children on sight. Have nothing visible to tie your group together if you gather somewhere in public.