A data centre cooling system problem halted futures and options trading at the Chicago Mercantile Exchange for several hours.
The issue, which lasted for around 10 hours, disrupted trading in markets across Asia and Europe, with participants unable to trade contracts tracking the S&P 500 Index and other assets.
Trading in stocks, bonds, commodities and currencies was affected before the issue was fixed at around 13:00 GMT.
The cooling system malfunction happened at a data centre operated by CyrusOne in the Chicago area.