Nasdaq says software bug, Arca issues led to trading outage

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Nasdaq OMX Group said on Thursday its massive trading halt last week was due to an internal software bug and other technology issues triggered by problems at NYSE Euronext's Arca exchange that led to the failure of a key backup system.

Nasdaq said connection problems between Arca and the Nasdaq-run Securities Information Processor, or SIP, the system that receives all traffic on quotes and orders for stocks on the exchange, led the processor to become overwhelmed, forcing the exchange to halt trading in its listed stocks.

(Video: CNBC's Bob Pisani on what Nasdaq's doing to fix the issue.)

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