There's always been an issue with how you type on a keyboard. Unguarded, that can be fairly characteristic of who you are, and it's easily measured by remote programs. The huge flaw in all these things is the false-positive, false-negative rates and how to deal with them. It's been the death knell (fortunately) of many of these schemes where they expect to distinguish an individual from all others on the planet. Repudiation is kind of difficult too.
