High frequency traders, using powerful computers to trade in nanoseconds in high volume, are courted by exchanges because volume equals profits.

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Alliance Tech claims its system is the first radio-frequency identification (RFID) system to track trade show and conference-goers.

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Accelerating the declines, high-frequency hedge funds, which use computers to trade at super high speed, appeared to pull back from the market as prices collapsed.

WSJ: Dow Takes a Harrowing 1,010.14-Point Trip

Others worried about the hyperactivity of high-frequency traders have suggested charging them for each trade they break, although that would not necessarily improve liquidity and is an idea that is unlikely to be pursued.

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The frequency depends on the holdings and your tendency to trade.

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The issue becomes just the latest in a long list of issues the SEC is examining regarding the current U.S. market structure, right up there with high frequency trading, dark pools, flash trading, market access, and trade tracking and reporting.

FORBES: SEC Takes Aim at Wild Market Swings

Regulators are looking into whether exchanges, in a rush to gain the business of high-frequency firms, have provided advantages to some sophisticated trading firms that allow them to trade profitably at the expense of other investors, according to people familiar with the continuing probes.

WSJ: High-Speed Trading in the Spotlight

He says many ETF firms court high-frequency traders, which help provide the buy and sell orders that can make ETFs easier to trade for other investors.

WSJ: High-Speed Trading in the Spotlight