That wouldn't be difficult provided there is an intention to do so. Quite naturally, if you are earning just enough to provide for a living and not the one like that of a millionaire, it is not very likely the tax authorities will be interested in the source of your income, though your mileage may vary. But if it is measured in the range of millions, they may get interested, then you have to answer some questions asked and you'd better have the required taxes paid to get off cheap and unscathed. They can easily find out when you decide to cash out as all big transactions are recorded and then thoroughly analyzed for money laundering and similar criminal activities.