Regulators are increasingly worried that Bitfinex, a widely used (and famously opaque) exchange, has been propping it up. The Commodity Futures Trading Commission has subpoenaed the company, whose Tether digital token is often used to buy other virtual currencies. Hundreds of millions of dollars worth of new Tether were created; almost always when the prices of other virtual currencies were heading down. The Tether were used on the Bitfinex exchange to make big purchases of Bitcoin and other tokens, helping push their prices back up, according to multiple analyses of data from Bitfinex.