Published 4:27 PM ET Mon, 8 Oct 2012 Updated 7:28 AM ET Tue, 9 Oct 2012 CNBC.com 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-milli
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