https://www.vice.com/en_us/article/k7enqn/google-is-letting-people-find-invites-to-some-private-whatsapp-groups

Google is indexing invite links to WhatsApp group chats whose administrators may want to be private. This means with a simple search, random people can discover and join a wide range of WhatsApp group chats.

"Your WhatsApp groups may not be as secure as you think they are," Jordan Wildon, a multimedia journalist for German outlet Deutsche Welle, tweeted on Friday. Using particular Google searches, people can discover links to the chats, Wildon explained.