Why is QsslSocket working with Qt 5.3 but not Qt 5.7 on Debian Stretch?

Question

I have an app that uses the QWebSocket class but not SSL. It works fine when I execute a version compiled with Qt 5.3 but a Qt 5.7 executable freezes on the following warnin

Answer 1

You have to install the following package with the following command in order to fix the problem:

sudo apt install libssl1.0-dev