Don't believe the incorrect flight plan malarky...seems an incredulous reason for a whole system failure. And if it was cyber, would they actually admit it?
Truth is probably much more mundane though...in my old company, the entire IT infrastructure was collapsed for a number of days after an employee tripped in the server room and landed against an emergency stop button (you could not have written it, but it was captured on CCTV). The resulting shutdown was 'dirty' and caused absolute chaos...