Never a virus, but I have messed up my laptop twice installing OSX and it would not boot up. I dont know why though, I installed it fine and my hardware was compatible, I would either get it stuck on the apple logo which I could fix or it would get stuck at the screen right at boot up which said "ACER" and had the BIOS F keys to push, I couldnt get past this screen when this happened and it had to be rebuilt.