I think bitcoin is a world currency not a private currency and because he does not hold by the government and does not have tax.. and i am agreed for this currency. so all people are wrong tell us bitcoin is a private currency.
For the word "world currency" then its not applicable yet not all people do have such possession of bitcoin and when we do talk about generally with currency then it is just good on digital and its not being regulated or being controlled or owned by anyone. The only private thing here is that you can have those coins without even knowing your true identity and you can really have that full control of your own funds.