If anything they'll make a program that buys when you buy and sells when you sell. If all your orders produce double prints on the T&S something is up.
Brokers do not need to steal any systems because unless these systems are really remarkable and enough diversified in terms of different accounts, just taking the other side over a long period of time will render all customer systems unprofitable and they know that so they do not bother because in the first case they cannot do anything anyway and in the second case they will get back all the profits sooner or later.