In this year (248 CE), a sect of heretics appeared which said: "He who apostasises with his mouth, refuses to recognize God and hides his faith in his heart, is not an infidel, because his faith is in the thoughts of his heart and his desire; it is the same for incredulity." They put about on this subject a book where they tell that he who reads it and listens to it, receives the forgiveness of his sins. They did not accept any of the prophets and apostles [Agapius Universal History]
One could argue that the context of the narrative identifies these crypto-Christians as residing in Alexandria as it is squeezed between the beginning of Dionysius's reign as Pope and Antony's establishment of monasteries in the Egyptian desert.
My point of course is that we see the crypto-Christians THROUGHOUT the period dating back to the time of Clement. Clement was a crypto-Marcosian. Origen was a heretic pretending to be Catholic. Origen's master Ambrose was a crypto-Marcionite (I happen to think 'Marcosian' is the Greek way of rendering the Aramaic 'Marcionite'). Dionysius is another crypto-Christian.
The world hasn't woken up to the fact that the Alexandrian Fathers were just 'going along' with all this 'the representative of St. Peter is our leader, just like Mark was Peter's towel boy' bullshit. Why so? Because they were scared of being brought before the Roman magistrates, that's why!
I have always known about crypto-Jews because I happen to come from such a family. Then I was surprised to learn that there was a parallel phenomenon to the Dönmeh among the Greek Christians of Turkey who were forcibly converted to Islam.
The bottom line is that only Western scholars who were so used to being 'masters of the universe' and thus utterly alienated from the reality of oppressed minorities would have a hard to time reconciling the idea that the original followers of tradition of St. Mark could have to go 'underground' with their beliefs once Commodus decided to actively 'correct' heresy (i.e. 'diseased' forms of the religion which went against the proscribed orthodoxy).
Life about suffering as the founder of another major religion noted. Western scholars just don't have the correct set of life experiences to understand the 'so-called heresies' properly ...
Stephan Huller has had a life long interest in religion and spirituality 
dating back to conversations with his grandfather, Gaston Frank. "He said we represent one of the last descendants of the Frankist Jewish faith in the world," he muses. "I grew up thinking that our family was something like the Last of the Mohicans."