Given the volatility of Bitcoin in recent months, the appeal of a cryptocurrency dubbed a "stable coin" is understandable.
That was the thinking behind Tether when it was first launched in 2015. Yet the reliability of the digital currency is now being questioned, raising fears it could severely affect the price of Bitcoin and impact many exchanges.
The announcement that the US Commodity Futures Trading Commission sent subpoenas on December 6 to virtual-currency venue Bitfinex and Tether rattled investors, sending the bitcoin price down to two-month lows.
Here's what you need to know about the mysterious currency.
What is Tether?
Tether, also known as USDT, is a cryptocurrency that started trading three years ago. The company behind it claims it is pegged to the US dollar. As such, it is intended to have the stability of the dollar but the ability to be used as a digital currency.