> HFT is responding to information about trades that have already happened (possibily at a different exchange). And that they were likely a party to. They wou

> HFT is responding to information about trades that have already happened (possibily at a different exchange). And that they were likely a party to. They would place small orders on all the stocks so that they could detect activity that they could exploit at the next exchange a millisecond down the wire.