Japan stocks rattled by $617bn 'fat finger' trading error

A trader points at a computer screen Image copyright AFP
Image caption The "fat finger" mistake refers to a human error made by mis-typing a trade

Japan's stock markets were rattled after a trading error caused more than $600bn (£370bn) worth of orders to be made and then cancelled.

An anonymous broker entered an over-the-counter trade for 42 stocks before swiftly cancelling it on Wednesday.

The transaction affected huge volumes of shares in blue-chip stocks such as Toyota Motors, Honda and Nomura.

Japan's Securities Dealers Association (JSDA) confirmed the mistake.

"A member company traded 42 issues at the off-exchange transaction at 09:25 on 1 Oct, 2014," JSDA said in an emailed statement. "This was, however, their error."

"After all of these reports were cancelled at 09:43, the revised correct report was made at 13:44".

The so-called "fat finger" mistake, which refers to a human error made by mis-typing a trade, was for an order worth more than the size of Sweden's economy.

The biggest order was for 1.96 billion shares of Toyota Motors for 12.68 trillion yen.

Image copyright AFP
Image caption Japan is the world's second-biggest equities market after the US

Some previous incidents of computer errors have resulted in severe consequences.

In 2012, US market-maker Knight Capital Group almost went bankrupt after it lost more than $450m when its computers made erroneous orders that couldn't be undone. The firm was later sold.

Japan is the world's second-biggest equities market and has seen an exponential increase in the amount of trading done electronically.

A lot of electronic trading takes place off its exchanges, or over-the-counter, and orders to buy or sell stocks are submitted and withdrawn regularly.

Brokers are required to file a report within five minutes if there is an error. However, the size of Tuesday's cancellation was unusual and took traders by surprise.

Japan's benchmark Nikkei 225 index fell by 0.6% on Tuesday, but its decline has been attributed to poor economic data.

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