I used to work with someone who had a collection of fridge magnets on the side of his PC.
As I was the IT admin at the time, as soon as I notice this I pointed out to him that it *may* not be the best place to keep them and he totally shot me down in flames insisting that there's no way it could harm anything as they were only fridge magnets and the PC had very solid steel sides.
A couple of weeks later he came whining to me that his PC is acting up and it looked like his hard drive was corrupted. Of course there's no way of knowing what actually caused the issue, but I told him there wasn't anything I could do beyond a reformat and reinstall do as some numpty had stuck magnets to it.