Back when I was in the IT game, I was working for Islington council on a project they were running to promote better use of computers in small businesses. Got sent to this wedding dress shop in Finsbury Park because she was having problems with her PC. OS was basically corrupted beyond repair, so performed a fresh install (giving her a newer version along the way). She was happy as larry, so off I went job done.
Couple of weeks later got this call from her saying I had caused her monitor to blow up. Asked wtf she was talking about, turns out her monitor had blown up a couple of weeks after I had fixed her machine. Yeah, and whats that got to do with me? I replied, Well, says she, she had been into PC World and some gob ***** had told her the reason it blew up was because I had upgrade the OS. I asked her to accompany me along to PC World so I could tell the person who gave her such excellent advice, exactly what I thought of him. Funnily enough she did not go along with that idea.