The US Securities and Exchange Commission (SEC) is reportedly investigating the links between computer trading companies and stock exchanges, to see if they have unfair advantages over other investors.
The SEC told the Wall Street Journal it is focusing on the ownership of some automatic trading companies and any ties to the exchanges themselves, although no allegations of fraud have been made.
Daniel Hawke, head of the SEC market abuse enforcement unit, told the newspaper: "We're interested in understanding the ownership structure and history. How the firm got started, who was behind it and who wrote the [computer trading] code that might be at issue."
Hawke is overseeing around 20 probes into computerised trading, the paper said.
The May 2010 "flash crash" - which saw high-speed computer trades bring the market to its knees in a wave of rapid selling - sharpened the focus of the SEC and other US regulators on automatic algorithmic trading.
In February this year, the European Commission urged tougher rules on computerised trading, including better monitoring on access to commodities to stop "speculative" traders from building up large positions that affect food and energy prices.
A "rogue algorithm" will cost a financial institution a billion dollars or more in 2012, Progress Software recently predicted.