Entanglement seems like a very good way to secure data and other things in theory, but you would have to log the 2 or more states of the objects. In this case most likely electrons or photons. The implementation of this could be a weakness.

Say you have 2 electrons one is spining down, and the other is spining horizontaly left to right. You would have to log this some how inorder to unlock it for comparison later. Where ever this is loged would be my target as a hacker.

It is true the two states are un predictable, but you might not have to predict if you can find a refference. Also what is to stop brute force? In quatum computing there are 4 posible states for each bit. So for 2 states(2 bits) leave 16 possabilities. So for 128 bit encryption..

That leaves 268,435,456 possible combinations. I can see a brute force doing that in maybe an hour or 2.
My New site OpenEyes