Bitcoin “is a fraud” and will blow up, Jamie Dimon, chief executive of JPMorgan Chase & Co (JPM.N), said on Tuesday.

Speaking at a bank investor conference in New York, Dimon said, “The currency isn’t going to work. You can’t have a business where people can invent a currency out of thin air and think that people who are buying it are really smart.”

Dimon said that if any JPMorgan traders were trading the crypto-currency, “I would fire them in a second, for two reasons: It is against our rules and they are stupid, and both are dangerous.”

Dimon’s comments come as the bitcoin, a virtual currency not backed by any government, has more than quadrupled in value since December to more than $4,100.

Bitcoin is a digital currency that enables individuals to transfer value to each other and pay for goods and services bypassing banks and the mainstream financial system.