The second-largest cryptocurrency exchange, Bithumb, has been accused of faking trading volume over recent months. Korean-based Bithumb is denying any wrongdoing.

A little-known exchange ranking service based in Ukraine, CryptoExchangeRanks (CER), has published a report that claims Bithumb may have been wash trading to achieve the top spot in the exchange rankings during October and November 2018.

According to the report, Bithumb’s trading volume in September 2018 placed it at the bottom of CoinMarketCap’s top ten with daily trading volume of around $350 million. In early October daily trading volume increased to over $1 billion, rising further to over $4 billion in November. This growth then placed Bithumb at the top of CoinMarketCap’s charts by exchange-reported trading volume.

CER says it studied Bithumb’s 10 most active coins over different time frames, looking at historical trade data from 2018, and calculating the correlation between trade volume and price volatility to determine something called “price-volume correlation” (PVC). CER says the PVC fell to a value in September 2018 it considers “influenced by non-market mechanisms.” CER said:

“The obtained results suggest a high chance of foul play taking place on Bithumb since the lower the PVC value the more likely trade manipulations have taken place.”

CER’s report and accusations, published December 19, says of bitcoin (BTC) trading: “Our analysis suggests that the trade volume has been intentionally inflated on Bithumb starting from the end of August and continued even today.”

The report goes on to analyse bitcoin trade volumes and average transaction size (ATS) for the period, looking specifically at certain days. As one example of CER’s findings, on September 9, 2018, there was “an extraordinary pattern, a period of intensive trading activity with a great number of large trades and varying trade sizes.” This intensive trading lasted five minutes. CER said:

“During that incredible outbreak, almost 7,500 trades (39% of the day’s total) were carried out with total volume of 34,600 BTC that accounted for over 94% (!!!) of the whole day’s volume. ATS of trades was 4.62 BTC, while ATS over the rest of the day – only 0.15 BTC.”

As this entire market manipulation continues, CER asks: “Why does one of the leading Korean exchanges operating in regulated jurisdiction and reporting solid profits for the first half of the year allow itself to engage in such malpractice?”

Manipulation, or wash trading, can occur if coins are bought and sold at the same time by an exchange, bots, or other actors, in order to portray much higher trade volumes. This can influence coin price and market confidence. Indeed, CER’s marketing lead Gleb Myrko told a Forbes contributor its “multifaceted” investigation points to trade volume and manipulation, “specifically, wash trading.” Myrko also concluded that the increases in trade volume were “not linked to price fluctuation on the exchange.”

The Forbes contributor did gain a response on the accusations from an “unnamed company representative” who reportedly said that “Bithumb is doing nothing to inflate trading volume.” He also questioned CER on its motivations for the report. CER is part of Hacken Ecosystem, which has its own token, although it has apparently never tried to list its token on Bithumb.

A report published this week by the Blockchain Transparency Institute said that wash trading is common and that 87 percent of the transactions at top exchanges are fake. As reported in May 2018, the Department of Justice (DOJ) and Commodity Futures Trading Commission (CFTC) have been investigating incidences of wash trading that may have influenced the price of bitcoin