WhatsApp is secure and uses good, verified end-to-end encryption. Media buzz in 2017 was about a design decision that theoretically enables the security keys to be changed without the user knowing it. To protect ourselves from this unlikely possibility, everyone should (DO THIS NOW!):
In WhatsApp, select Settings in the lower right
Select Account
Select Security
Turn on "Show security notifications"
With this setting enabled, if the security keys are ever changed then you will see a message that states 'security code changed' (as shown in the attached screenshot).
This message can appear for a couple reasons:
The sender got a new device or reinstalled WhatApp and the keys were changed automatically.
The government has coerced WhatsApp to change the keys.
Number 1, is the reason WhatsApp decided to design the software this way. In the unlikely case that number 2 occurs, you will see the 'security code changed' message (assuming you followed the steps above).
If you ever see the 'security code changed' message, stop using the app until you can confirm if the sender got a new device or reinstalled WhatsApp.
The messages are not stored on the server (like they are with Facebook Messenger, etc), so the government cannot go back and read old conversations. The worst case scenario is that they will be able to read only one message (as long as you stop chatting when you see the 'security code changed' message).
WhatsApp security is actually better than iMessage in some ways:
Here's the response from the company that wrote WhatsApp's encryption software: