One Algorithm Made Up 4% of Quote Traffic Last Week

Thanks to Will for passing this along.

A single mysterious computer program that placed orders - and then subsequently canceled them - made up 4 percent of all quote traffic in the U.S. stock market last week, according to the top tracker of high-frequency trading activity. The motive of the algorithm is still unclear.

The program placed orders in 25-millisecond bursts involving about 500 stocks, according to Nanex, a market data firm. The algorithm never executed a single trade, and it abruptly ended at about 10:30 a.m. Friday.

"Just goes to show you how just one person can have such an outsized impact on the market," said Eric Hunsader, head of Nanex and the No. 1 detector of trading anomalies watching Wall Street today. "Exchanges are just not monitoring it."

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Related previous post: Chris Martenson interviews Eric Hunsader