South Korea's government has been signalling that it plans to crack down on cryptocurrency trading.

Exactly how it will do this remains vague. But just the threat of action has been enough to drive a sell-off across the market globally.

Bitcoin, for example, has lost nearly a quarter of its value in the past week. And so on Wednesday the virtual currency - which last month looked set to breach the $20,000 (£14,500) mark - was trading closer to $12,000.

Prices of cryptocurrencies are volatile at the best of time. Rises and falls of 10% or more in a day are not uncommon. And pinning down rationale for those sharp movements often involves guesswork.