https://www.cbc.ca/news/technology/whatsapp-spyware-infect-call-1.5134939
That's a link nto an article talking about spyware that can be installed when you have WhatsApp installed, your WhatsApp number gets called, and you don't answer. I haven't seen any technical discussion on how this is possible yet, but holy cripes, that is a wide-open security hole...
I imagine it like sends some kind of graphic or script or /something/ that can be exploited when a call is missed. The phone displays it and wham. Gifs and pngs have been exploited that way before, in fact i think older versions of android's image loading code is known to have code execution exploits.