That's not what is normally referred to as a 12x12. That term usually refers to a puzzle like this one:
http://www.websudoku.com/variation/?day=3Furthermore, the puzzle in your image is a killer sudoku AND a diagonal sudoku (aka sudoku-X). I've never seen killers other than 9x9 (including multi-grid variants). I'm pretty sure you're not going to find any software that handles puzzles like these. Where did you find this one?