The price of a Bitcoin has jumped from $13 at the start of this year to more than a thousand, and it's still rising. Congress and federal regulators are beginning to pay attention. There already are Bitcoin millionaires — and Bitcoin criminals -- even though most people don't understand what a Bitcoin is. We hear about digital currency, controlled and stored in computers and traded across the Internet as a way to make payments. How does it work? Is it really safe? Is the value of Bitcoins subject to the old adage: what goes up must come down?