Which trading error caused Knight Capital’s $440 million loss during the 2012 stock-market disruption?

A software deployment error caused Knight Capital’s $440 million loss during the 2012 stock-market disruption. On August 1, 2012, faulty software activated an obsolete function in Knight’s trading system, causing it to send millions of unintended orders.

The malfunction affected 148 companies and lasted for about 45 minutes. Knight accumulated large positions while its automated system bought and sold shares abnormally. The firm lost approximately $440 million, an amount that threatened its survival and led to its later acquisition by Getco.

The event exposed the risks of automated trading and inadequate software controls. It was not caused by a market hacker, a rogue human trader, or a Federal Reserve announcement. The Securities and Exchange Commission later examined the incident, and the episode became a prominent example of how a technical deployment mistake can produce market-wide disruption and enormous losses in a short time.