Fascinating article, though now the SEC is discussing a potential ban on this, mainly looks to impact big firms that use automated systems:

what flash trading is:
http://www.cnbc.com/id/32122827/

potential ban:
http://www.cnbc.com/id/32895900

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p.s. per sec/cftc/ftc regs, none of this is to be construed as trading recommendations, it's just for educational use only, so you can "peek over my shoulder" to see what I'm doing with some of my trades. See www.daytradingu.com/disclaim.htm for full disclaimer.
These pages contain excerpts of actual trades I've made; it's not a complete record of every single trade I make. Some days I'll take trading wins or losses that I do not take the time to screencap and post online; it's a partial record of some of my trades. Note that I am not making income nor profitability claims of any kind. Most traders lose regardless of what they do. The majority of my personal income comes from my training business. I try to capture the best highlights of successful days so you can see practical examples of what I'm trading. There are also days in which I incur losses (and wins) which are not shown. This is simply a partial record showing highlights of some of my successful trading days. No representation is being made that other traders, including customers, will be able to trade like I do. Generally expected (average/typical) trader results are that all traders incur trading losses and most do not become profitable, regardless of the training they get. Trading is a speculative, high-risk activity.