A huge order for the OMXS30 December future in Stockholm this morning forced Nasdaq OMX, the operator of the local stock market, to shut down trading in derivatives.
The problem occured when the trading system received an order for more than 4.2 billion contracts on the December future.
Each contract is worth some SEK107,000, which made the value of the full order more than 130x Sweden's entire GDP.
Somehow the order made its way into the order book, causing chaos for traders.
Local media are quoting spokespeople for the exchange operator as saying that it is carrying out an investigation, and that it does not want to allow trading to begin again before it knows what went wrong.
The order book system is meant to filter out orders that look abnormal, but in this case it did not work.
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