[thaumasiotes]

Based on your parent comment...

> This is really sad for people like me who don't want to install WhatsApp on their phones because it sends too much of my data to Facebook... probably that's precisely why they are so strict, to get all the data because that's all they get (the service is gratis after all).

When you send a message through WhatsApp, WhatsApp knows you sent the message and who you are.

Since they know who you are, they also know, independently of the request you just sent, whether you're using their official client, and what data they've managed to extract from your phone.

If I get a seemingly-valid message from you despite the fact that I know perfectly well you've never installed my official client, I'm going to conclude you're not using my official client.