Ann: Change in substantial holding from Galaxy Resources,GXY-GMM.AX, page-5

These are the 'bots' high speed algorithmic traders that are designed to make small margins through manipulating the price. They prey on the retail traders and will often slowly accumulate as they churn the volume to increase uncertainty in the market.
They pay a fee to the ASX to have their computers located near the ASX machines. They can see your buy and sell orders before they hit the ASX and respond accordingly.
They should be banned but the only way this will happen is through legislation change - ASIC will do nothing and the ASX will not give up the revenue!
In the US they are getting closer to being banned.

Simplistically in my mind you do not pay the ASX to locate for 'nearness' if there is no advantage!