Check if there is a tax treaty between Oz and your country of residence. If you were resident in Canada you are required to pay tax on world income, including gains on investments in Oz, and would not need to submit an ATO tax return. Your situation may be different, depending on your country of residence. The Oz banks will almost certainly disclose your transactions to the tax authorities in your country of residence. In the western world it's the close knit combination of banks and governments that keeps all us plebs paying our taxes. As Wikileaks Assange said, 'the western world has fiscalised its relationships'.