I always wondered about this topic myself as well. Not that I was wise enough to inveset in BTCs a year ago, so I unfortunately do not have this kind of problem (yet). But I am half scared that even if I would try to pay the taxes and get it to my bank account as legally as possible, the explanation of "I invested in BTCs when they were low and sold them high" would not be understood by the tax agency and would try to probe me for money laundering or drug bussiness or something like that..