My friend is part of a business of about 10 people that provide stock and share advice to paying members in a Telegram group. It's a quite expensive pay monthly group of loyal enough customers who benefit from the group's secrecy and so a leak compromises the success of the group. There are over 200 members in the group currently. Recently a user within the group has been leaking this information to a Discord channel and charging non-members a fee to access to it.
My friend found out who the user was but it appears they have multiple accounts still running and hidden throughout the current 200 users. They appear to be using bots to glean information directly from the group.
How could we catch these information leaks using some kind of trickery and subterfuge such as a canary trap? A canary trap is likely not possible as each user of the group receives the exact same information via the group chat so that option is likely out but there must be some other sneaky way.
The vetting process to enter the group is very strict so once we can identify this user and all associated accounts we should be able to ban them permanently.