Is there anyone who has encountered this on the wallpaper ...

 Observer
Is there anyone who has encountered this on the wallpaper ...
a black spot appears on the wallpaper next to the computer to check it was rearranged and the same story, what could be the matter in your opinion?

Answers:

dragonfly
sitting at the computer touches the wall with his hands (feet, head ..)

gossamer
Accumulation of dust from electrification.

Sasha Sh.
Do you have a computer system unit? Then the very first thing that comes to mind is that the cooling fan drives air, which captures the accumulated dust inside the case and it settles on the wall. Keep your PC clean and do regular wet cleaning in the room. But the fact that the spots are black, an alarming symptom (household dust is gray or brown) - this is how mold, fungus appears due to infection from some source and high humidity. Owners of air conditioners who neglect to clean it often encounter this phenomenon ... If the stains are single, it may be easy to get rid of them by simple cleaning with cleaners and disinfectants. https://dzen.ru/media/id/5c9f240271bbe600b33bab11/chernye-piatna-na-stene-plesen-dumali-pridetsia-meniat-oboi-no-vopros-reshilsia-za-15-minut-i-200-rublei- provereno-rabotaet-613dc2ce24a814192e119b8b

Alexey Kuznetsov
unfold the system unit so that the dirt from the cooler does not fly

Irina Baron
Large calendar and hang on metal tape.

MONKEY
Shadow?