Hi, i want to know the best way to make a register system, that's will be very hard to hack, and what i will need, some books for help me, some sites, any way to helpme, and some kinds of tricks of how to use others way to find you friends, like, if two members, friends on facebook, register on my site, they will get a notice that the friends has make the new account, or the new when create the account find every person in the moment that he create(like on facebook) or both... thanks