[reverend_gonzo]

HFT firms don't see the buy order before its get to the market. They see that a bunch of quantity was bought so they raise their prices on the other markets. Because the purchaser had bad order routing, he moved the market and the hft firms were able to raise prices for what they believe the new market price to be.

Say you decide you want to buy up a bunch of property that's all on one street, and the market price for each property is listed at $100,000. Once word gets out that you made the first purchase for $100k, the prices on those other properties are going to go up, because if there's a buy at $100k, they might as well start negotiating at $110k, but they have no idea if there's a buyer who wants just one property, or all of them.

Now, only the buyer know how much he wants to buy. If he was smart, he'd go to each seller and execute at the exact same time so when word gets out of a purchase and prices go up, he's already purchased everything he wanted, the uptick in market prices actually benefits him.

It's the same thing with trading. If the guy is buying a couple thousand shares scattered across a dozen exchanges, he absolutely needs to make sure they get posted to the exchange at the same time, or he needs to break them up in small orders over a period of time so he doesn't affect the market with his purchases.