Sites normally employ various mechanisms to prevent session fixation attacks[1] and similar malice. These mechanisms prevent session collisions as a side-effect

Sites normally employ various mechanisms to prevent session fixation attacks[1] and similar malice. These mechanisms prevent session collisions as a side-effect, thus your scenario seems rather unlikely. [1] http://en.wikipedia.org/wiki/Session_fixation http://en.wikipedia.org/wiki/Session_fixation