A secret program called "Project Ghostbusters" saw Facebook devise a way to intercept and decrypt the encrypted network traffic of Snapchat users to study their behavior.
Facebook achieved their MITM attack by selling a VPN with spyware in it.
And so you have to wonder: who in his right mind would buy a VPN service from effing Facebook of all companies? It's like asking the KKK to do the catering at your bar mitzvah: if you have a problem with the service, you kind of asked for it.
it was a free app, wasn't owned by Facebook from the beginning (they've acquired it in 2013), and it offered data saving, so it was a tempting install for people with small data plans.