I think there is a hacker in my game?

You can send a report ingame about it and a GO will see if there is a hacker or not. You will get a update and a message from the report you made.

May I ask what do you mean by "Hacker" ?

If it's someone who is growing much faster than you, could be you have a good player on your map who knows what to do, or they are using Gold which is a feature of the game that would allow for faster growth.

Both are just normal parts of the game.