Sudoku

Try to fill every empty square with number from 1 to 9.

You must obey following rules:
1. Every row must contain numbers from 1 to 9.
2. Every column must contain numbers from 1 to 9.
3. Every 3x3 square must contain numbers from 1 to 9.

There's also a mysterious code. What could it be?
Psst. You can ask the developer.

Enjoy the game!