Have you already sth. like an example of this system you've made on the net.
I could test it!
Because I could imagine a way of how to hack you but I'm not sure if that what you've made fits the case.
2nd THERE IS ALWAYS A SMALL POSSIBIILTY OF BEING HACKED as long as using PWs but today we have no other possibilyties. So the safest system is UNIX PW sys you maybe saw it on private sites or poen sites which you have to pay(the dialog asking you for name and pw).
Maybe in the next future it will be already possible to have a scanner detecting your unique fingermark but always remember:
IT IS IMPOSSIBLE TO HAVE A 100% SAFE SYSTEM!!!!!!!!!!!!!