The question is whether crypto traders have been using well-known tricks to raise the prices of the currencies. In particular, the report cites spoofing, where orders are placed and then canceled once a price changes, and wash trading, where a trader sells to themselves to give the impression of market demand.

Bitcoin fell on the news, to $7,337, as of Thursday morning. Ether fell to $566.

This isn’t the first time that we’ve heard about price manipulation of digital currencies. In January, concern surfaced that activity on the virtual exchange Bitfinex had helped prop up the price of Bitcoin.

Regulation of cryptocurrencies is still relatively weak, at least in the U.S. So far, the Securities Exchange Commission and the Commodity Futures Trading Commission have focused on initial coin offerings, the sale of digital tokens as a means of raising money.

Other countries have taken direct action against cryptocurrency exchanges. For instance, China banned them.

According to Bloomberg, the Justice Department is working with the C.F.T.C., which can’t directly regulate the trading of cryptocurrency tokens because they’re not futures. But the commission could impose sanctions if it finds evidence of wrongdoing.

If it is found that prices have been manipulated, DealBook wonders if criminals have been at it recently. If so, they haven’t been doing a very good job: The price of Bitcoin has fallen by about half since its peak in December.

— Jamie Condliffe

Nathaniel Popper of the NYT offers up his take: The DOJ is looking at traders trying to manipulate the virtual currency markets through sophisticated trading techniques, according to this story, but much of the manipulation goes on, out in the open. Going all the way back to 2013, I reported that virtual currency markets were subject to pump and dump schemes that were promoted on Twitter and other social media. The problem has proliferated since then, as BuzzFeed reported more recently. It will be interesting if prosecutors decide to go after traders and leave this more visible activity untouched.