I do not know but why would it become the biggest risk to civilization aside from helping us in some job.  Maybe it will dominate the livelihood or certain jobs of human and then yes, I will agree.  But considering they are robots and human made them, then it will not be a threat.  You can destroy them using certain commands or spill some water to them and then they will die.   I still believe that it will not be a threat.  Humans are still great than anyone here on earth.