Bitcoin is a virtual cryptocurrency present in the game. Bitcoins can be traded for in-game money (or vice-versa).
Bitcoin has unique anonymous features.
The only way to login on someone's else wallet is by sighting it's key on the victim's log. This happens when:
A wallet is the equivalent of a bank account. The wallet is stored on your software page, and publicly lists how much BTC you have on it.
The value of 1 BTC is the same of real life's bitcoin buy price. (It might be rounded).