The digital currency Bitcoin has moved from the fringes to more of the mainstream in the past few weeks, mostly because its value has risen at such an extraordinary rate. And just like a surging stock, it's left a lot of people wishing they'd either got in earlier, or wondering how they can jump on board now.
But as ever, there are questions about how safe it is, how to regulate something which by its very nature is decentralised, and if it is just another bubble waiting to burst.
So, what is behind the sudden rise in value of Bitcoin?