A worrying new WhatsApp glitch has been reported by Joseph Cox at Wired magazine. This glitch can let anyone find and join your private group chats without your permission. Whatsapp have not fixed this issue yet and as soon as they do I will let you know. In the meantime here are a few things to keep in mind:
1. Any group chat you are in right now can be easily found online.
2. Anyone who finds a chat that you are in will be able join the chat and will also be able to see contact info for everyone in the group.