US Treasury Secretary Janet Yellen on Monday termed cryptocurrency bitcoin as an "inefficient way of conducting transactions". She was speaking at a virtual conference on Monday hosted by the New York Times. "Bitcoin is an extremely inefficient way of conducting transactions and the amount of energy that's consumed in processing those transactions is staggering," said Yellen. “I don’t think that Bitcoin is widely used as a transaction mechanism,” she added. Her remarks added fuel to the fire and was one of the main reasons for a drastic fall in its levels. The traders, however, say that the downfall is linked to sell-off in global equities which has curbed risk appetite. Some investors have also cited concerns about the rapid surge in the virtual currency's price.