Classic Sudoku is a truly challenging free online Sudoku game. To start with, even before you get into the game, you have to select which mode you would like to play. Depending on how good you are you can select Easy, Medium or Hard. Once you have selected the mode, you start the game. You have to fill in the number 1 to 9 in the columns and rows of the 9X9 grid and also in the demarcated 3X3 grids. The one rule is that in all these places, you cannot repeat any number. This is the challenge of the game. Sometimes you see that a number can fit into three or four places, and you have to decide where to place it; this is where the game becomes tough. When you want to input a number, simply click on a box and you will get a pad with the numbers 1 to 9 and you can select which one you would want. To get rid of the pad without making an input, you can click on the CANCEL button on the pad. In order to delete a number, you click on the DELETE button on the pad. This is a very interesting game in that you can even delete the numbers that you found in the puzzle at the start. This is a feature that is not seen in other games; you can end up changing the whole puzzle as you go along. The numbers that you place in the puzzle are the same color as the ones that you found so it may be hard to recollect where you put the numbers in case you want to make changes; but you could always create your own puzzle by even removing the clue numbers that were there to start with.