I had issue with update and in the end, had to send my Mac to technician who installed entire operation system back. When it came back, it was like first time - assign location in world, pick password, enter username etc. Does this mean it was clean install? Problem is, friend of mine managed to give me fear about someone else tinkering with my Mac and inserting trojans. While I know the likelyhood of technician ever doing this is near zero, the tiniest chance still makes me nervous. So according to this description, was my Mac clean installed and so it was impossible to insert anything bad in there before I brought it home and put new password and personal details in?