the 6 may 2010 cascading flash crash, page-9

Stop Loss Orders should remain secret and only known to the investor and the stockbroking house. Collusion between broking houses and hedge funds exposed these orders to the funds. Also fast buy/sell orders enabled funds to 'see' the Stop loss orders in the wings. Hence strategy could be planned via computer programs to trigger these Stop loss orders prematurely. Bombarding the market computers etc forced the market to crash and we know the consequences. Whether the plans to prevent this with circuit breakers is yet to be tested.