according to this post:
http://forum.enjoysudoku.com/viewtopic.php?t=3071they all have more than one solution. A sudoku puzzle should only have one solution which can be reached by using logic. If it has more than one solution there's some point where you can guess and still reach a solution.
You'll find lots of free and decent software here:
http://forum.enjoysudoku.com/viewforum.php?f=11for instance mine is here:
http://forum.enjoysudoku.com/viewtopic.php?t=4881it's quite a small download and a pretty strong solver. But there are many others
ab