The Dow Jones Industrial Average slumped nearly 1,000 points in a matter of minutes in the flash crash of 2010, sending traders into a panic and inciting scrutiny of the U.S. equities markets that's still being felt four years later.
The May 6, 2010, crash was initially blamed on a "fat-finger" error made at Citigroup—a theory that was later shot down and ultimately attributed to investment firm Waddell & Reed. But in addition to that trading error, a number of possible reasons for the crash has since come to light. One of those supposed causes was high-frequency trading, according to a report from the Securities and Exchange Commission that year.
Last week, in an investigation into unfair trading practices, New York Attorney General Eric Schneiderman's office reportedly requested information from exchanges and trading platforms regarding high-frequency trading firms.
And amid SEC accusations that it violated exchange rules, the New York Stock Exchange recently a $4.5 million penalty without confirming or denying the charges.