People who fix computers/laptops, what's the worst thing you found on someone's computer?

Somewhere I have a picture of it saved, but as a Sys Admin for an office one person had so much dead skin piled on their mouse I gagged. It formed the shape of their fingers on the buttons and the dead skin was, not exaggerating, like 4-5 millimeters thick of caked-on yellow disgustingness. Mind you, we provide new mice for people to use in the office for any reason, they just need to let us know and ask. There was no reason for this other than the person just being a Nurgle initiate or some shit. People are gross.