Information that is publicly accessible online can be indexed by Internet search engines such as Google, Bing or Yahoo. This means that information such as group chat invite links which were posted online on sites such as forums, blogs or social media, could be indexed and discovered. Such group chat invite links can be exploited by threat actors to join private group chats, without being invited by the chat administrator.
While it is common for some organisations such as clubs and associations to share their group chat invite links online as a way to invite members to join the group chats, organisations and groups that prefer to remain private should refrain from posting their group chat invite links on publicly-accessible sites.
To invalidate the links, the administrator may reset the group invite link (in WhatsApp and Telegram). The organisation or group can consider creating a new group chat as well.
Administrators of group chats are also advised to check their group chat member lists regularly, and actively monitor for any new joiners to the group chat, to ensure that there are no unauthorised members.