it's high frequency trading by algorithms, generally they are...

it's high frequency trading by algorithms, generally they are splitting their orders up into small parcels of shares. they do this so other traders don't recognise the true demand. in a sense it is computer algorithms, working against other computer algorithms. note also these high frequency traders don't have brokerage fees the same as general mum and dad investors

sometimes these frequency traders are pinging with buy or sell orders and cancelling these just as fast. in doing so they are testing the limits (buy or sell limits) and if they can push through them they are able to have a speed advantage of making a margin