There is a rumor that forex brokers literally can copy your trading experts strategy logic from MT4 and trade against you. Whether this is true or not I'm not certain though this may be very true, what I recommend is trading away from their server platforms and yet use their server data. The best way to do this is using a software called Fsb pro. It has a mode called trader mode by which you can connect MT4 Fsb connector that sends data to the platform and sends back buy and sell orders to MT4 without exposing your trading logic. Your trading logic remain on Fsb pro without the brokers knowing how you trade.