>DER SPIEGEL: But you do save data about your users like the device ID, the phone model, the WhatsApp user name, the phone book and thereby also the numbers of all their contacts, right?

>Cathcart: It’s true that we do have some information about how people use WhatsApp and that we do know, for example, the device ID. We collect this only to secure our services and protect from attacks. When you use WhatsApp and allow access to your phone book, we only see the phone numbers, not the name.

In particular, they have (meta)data regarding specific messages being sent, as evidenced by their approach to curtailing misinformation:

>Cathcart: Messages that are highly forwarded can only be forwarded to one chat since last spring. That led to a drop in 70 percent of these messages. More recently, we are additionally showing you a link to the Google search on those messages, to let you check the facts directly.

I'm not sure how easy it is to figure out whether those 'highly forwarded messages' are all the same, or somehow link them without knowing anything about their content or linking them to information you already know about people. Maybe it's easy and I'm making a mountain out of a molehill, I don't know.