Facebook doesn’t know your password…but they know if *you* know it. How?

No legitimate websites that require a password — Facebook, Google, Youtube…and millions more — actually know what your password is.

So, say you’re logging into Facebook but you mess up. You type your user name and then mistype your password. You get an error saying that the password you entered is incorrect. But if they don’t save passwords, how do they know?

Funny you should ask. The answer is quite fascinating, actually…