I'm here to tell you that Magnetronix are wonderful for the kids, Mr. C makes letters of them, and they stick to the fridge to be stored, but the kid just wants to experiment...in a way her mother would not have.
Stuck it right to the monitor screen. Left a purple and blue hue on the screen corner.
We did not know what to do for a while as it seemed permanent since it reoccurred in multiple windows. Happily a click off, click on of the monitor resolved resolution in our favor.
But next time he does that, I told him, they go in the trash.