Before we shine a spotlight on those who have left their faith – apostates – let’s start by looking at what’s driving them underground.

In Saudi Arabia it is a terrorist act to say that you're an apostate.

In Pakistan there have been 68 recorded killings related to apostasy in the last two decades.

In Australia, the vast majority of Muslims practice their faith peacefully. But a small, extreme Islamist group – Hizb ut-Tahrir – has openly declared that their interpretation of Islam calls for apostates to be killed.

For a few years now, I've been hearing whispers of a secret network of ex-Muslims living in Australia.

I did everything I could to reach anyone who knew anything. I wanted to understand why it was so difficult for young Australians to to turn away from Islam.

After months without a word, I got an email address from a young woman who told me to wait for instructions. A few weeks later I received a string of emails, texts and calls from people all over the country...

Ex-Muslims know the danger of speaking out.

These are just some of the threats they receive on social media...

Follow reporter Patrick Abboud undergound...