The combination of a username and password seems like an inextricable part of using a secured computer. Sure, you can use biometrics, but username and password just seems like the most natural way to identify and authorize users without the bulk of extra, expensive, and specialized equipment. That being the case, it has become second nature to most of us, but is it really natural at all? Memorizing passwords, especially "strong" ones, involves remembering long, arbitrary strings of seemingly random numbers and characters, hardly natural. That's why DARPA has undertaken an initiative to eliminate passwords altogether and instead identify users in the background, as they work, by paying very close attention to the idiosyncratic way they type.