Every one that is initially found and used by an attacker, up until it is detected. The exploit was a 0-day at one point in time. Furthermore, I'd argue that t

Every one that is initially found and used by an attacker, up until it is detected. The exploit was a 0-day at one point in time. Furthermore, I'd argue that the perspective of the one talking also matters. If Microsoft etc know about it, but haven't patched it or made anything public, it's definitely a 0-day if used against me, as I haven't had any opportunity to defend against it.