Can anyone clearly define what type of API orders are visible by others (the exchange?), and what type have absolute secrecy?
In general anything going to the market will be visible, although you can use things such as iceberg orders or similar to hide the true size of the order. Simulated orders which are simulated by the broker (such as stops on Globex at IB) do not go to market but are sent by IB as market orders when the stop price hits. If you're that concerned consider programming your own stop market orders -- when the price hits your target price, send it to market.... SSB
Should add that a lot of software packets has the logic in the client, for instance wealth-lab or Tradestation, meaning the orders are only known to you untill they trigger /DeltaDelta
Response to DeltaDelta: If I understood correctly from SideShowBob in a PM, if I place an order to buy e.g. options at bid price, along with a conditional cancellation (e.g. if underlying stock goes in the wrong direction), that the condition is not viewed by anyone, and no special software needed. Agree?
that conditional order would still be viewable by your broker. it may not be held at the exchange, but your broker can definitely view it (if they want to).