OK, I've heard of Facebook, but not WhatsApp. Apparently it's a messaging service (phones? computers? who knows!) that is "worth" the equivalent of £11,382,691,000!
That's almost 12,000 million pounds! How can anything really be worth that much?!
To get at least some return of investment Facebook will have to monetise the content of the chats.
BTW there are alternatives out there, which don't disregard privacy. Therefore I'm using Threema instead (have a look at www.threema.ch to find out more).