The internet does not explain what is dirt. Dirt or filth may be the evidence of IT or the spirit that they are always cleaning so I guess the dirt must not like to be made non-existent. As a retaliation, could this dirt be causing cancer if it is an intelligent entity? The dirt on the wall or floor or human body is not visible from a distance and want to be invisible to remain dirt to remain alive. I think the dirt on your computer screen does not want to be cleaned because it fears this elimination.