Online Windoku or HyperSudoku (Logical Thinking Puzzle Game)

This game is similar to Sudoku, except that there are extra 3x3 regions where the numbers must not repeat. In this game there is a grid of 9 x 9 squares, you need to fill in each square with numbers 1 - 9 so that the numbers in each row or column or each 3 x 3 group (the 9 groups surrounded by thick lines plus the 4 groups with the dark background) do not repeat. The faster you finish the game, the higher your score. Click the hint button when you are stuck, but you will suffer a time penalty when you do so.