I literally just got off the phone with a client who was worried that someone had snuck onto his computer and changed his brightness settings and font. I remoted to his PC to investigate. It turned out to be an email, where the sender was using a lighter colour for the font than he was used to. I tried explaining to him that the sender of the email had set the font and that no-one had changed anything. It took a while for him to believe me. In the end he hung up telling me to disregard the call.