uh, i don't know, privacy? being able to access a protected video w/o having the password shouldn't happen (what im getting from your OP is that you dont know the password)
and if im right, i dont think you'll find a program able to do that
i used to download youku videos but they are mostly fragmented so its a pain in the ass. and besides, it was years ago, i dont even remember the program i used.