Relying on unregulated infrastructure and exchanges is risky.

Most cryptocurrency trading happens outside the United States on exchanges with little or no regulatory oversight. That allowed investors to pile in with abandon, but the inherent dangers have long been clear.

This year, researchers at the University of Texas published evidence suggesting that one of the largest exchanges, Bitfinex, had helped create a proprietary cryptocurrency, Tether, that was used to artificially pump up the price of Bitcoin and other digital tokens.

Bloomberg reported on Tuesday that the Justice Department was conducting a criminal investigation of price manipulation using Tether, one of many issues related to Tether that are scaring investors away. Every unit of Tether is supposed to be backed by a dollar in a bank, but managers of Bitfinex and Tether have struggled to show that they even have bank accounts. Many traders have been selling Tether at a loss just so they can take their money out.

The activities of another large exchange, OKEx, have also led traders to question whether they can trust the institutions at the center of the cryptocurrency industry.

OKEx, which began in China, altered some trading rules without advance notice, according to a large hedge fund, Amber AI, which published a post on Medium about the changes. AmberAI said customers appeared to have lost millions of dollars because of the changes. OKEx, without acknowledging the losses, apologized to customers for some of the changes, which it said had been made to cope with chaotic trading.