Nearly identical trades in the popular online game Kalshi have drawn scrutiny from regulators and investors, who are investigating a $5 billion flurry of transactions that occurred on a single day last month.

The trades, which involved a series of nearly identical stock purchases by multiple entities, were executed through a combination of automated trading algorithms and human traders, according to industry sources. Regulators are taking a close look at the trades, which some have described as “high-speed” and “high-frequency”, in order to determine whether they comply with existing rules and regulations. Investors are also expressing concern about the trades, which were executed at prices that appear to be significantly lower than market rates for similar stocks. Analysts say that the trades may have been designed to create a false sense of market activity, or to manipulate the price of Kalshi’s stock in some way. The exact motivations behind the trades are not yet clear, but regulators and investors will likely continue to scrutinize them closely in the coming days and weeks. Multiple industry sources have confirmed that several major exchanges and trading platforms have been contacted by regulators regarding the trades, and that a number of investigations are currently underway.