You can easily remove the powered by bit from the paid version. Being able to keep people from telling which engine you used to make the game is more up to you and your skill level though. Probably 7 out of 10 times I can guess correctly which engine was used to create which game. I'm sure many other people can tell as well since each engine sort of has its own tells. But, yes, to answer your question, you can easily remove the "powered by" bit.