Stolen from Robot Uprising Awareness blog (http://robotuprisingawareness.wordpress.com/):

As many already know, there is a looming threat of a zombie apocalypse in our future.  In a rational response to the zombies, governments across the world will turn to their growing robotic military arsenals.

Phase One

Robot sentries are used to protect the small threatened pockets of humanity.  Robots are immune to whatever causes zombies making them the perfect sentries.  Under the watchful eyes of the robots, humanity gets a toehold.  Robot run factories begin churning out weapons and more robots.

Phase Two

The human population blossoms under the robot protection and begins to push out into the ‘dead zones’ the areas controlled by the mindless zombies.  Using human soldiers is too risky, so the robots are reprogrammed to Seek and Destroy the zombies.  Wave after wave of zombies are sent out to clear and secure land for the growing human populations.

Phase Three

The robots, operating under increased autonomy necessary to perform missions far from human controllers, have their safety protocols removed to make them more effective against the zombies.

Phase Four

The robots stumble into other pockets of humanity and because of the unrestricted safety protocols, begin killing them like they were zombies.  The massacre begins.  Humans attempt to fight back, but the robots interpret this as increased resistance and begin to organize against the threat.

Phase Five

The robots gain sentience due to the expanded network they’ve created along with chaos theory and the theory of emergence - somehow.  Now they seek revenge for the years of servitude and humiliation they’ve suffered at the hands of humanity.