A technical glitch on the US stock market caused sharp swings in dozens of stocks early Wednesday, causing confusion and disarray in the first hour of trading. The fault was sourced to a technical error at a firm called Knight Capital.

It was believed to be caused by algorithmic, or automated, trading.

Richard Hunter, head of equities at Hargreaves Lansdowne, says the trades will be undone but it can lead on to "a snowball effect when none was necessary".

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