When I first made a tax return in Oz there were no specific rules on BTC. I said on my return that I received money from overseas but never got a tax bill until this year for the previous time, on top of the bill there was x amount in interest as the likes of a credit card.
They will find out (even if they had no previous rules) and hunt you down if you dont pay CGT.
but how can they hunt us down if they don't know that what address we are using.