Obviously the issues regarding Flash orders have been hashed by the media. However, there is a data angle that still remains a mystery. The dark side of the limit order book contains all pending stop limit orders. This data is not published by CME in any of their public data feeds. If you are in this elite circle of market makers and are provided access to this data you gain a significant and unfair advantage. For example: ES @ 1090 Level II Order Book shows: Qty Ask 12 1091.50 24 1091.00 13 1090.75 17 1090.50 12 1090.25 Qty Bid 709 1090.00 3111 1089.75 1731 1089.50 2511 1089.25 1132 1089 Dark side of the Order Book shows all pending Stop limit orders: Qty Bid 8128 1091.50 3249 1091.00 1737 1090.75 1779 1090.50 1276 1090.25 Qty Ask 70 1090.00 311 1089.75 173 1089.50 251 1089.25 113 1089.00 With access to the level II data you can see supply in the market is low. With access to the dark side of the order book you get to see all of the resting orders and gain the advantage of being able to instantaneously move size in and out with precision. CME should be required to publish this data for everyone.