Story time: I've had my work laptop replaced three times in the past two years because of persistent crashes under load. We tried replacing a lot of stuff, uninstalled all kinds of software etc., nothing helped. Turns out they'd remotely installed some utility about five years ago that controls fan speeds. That has been installed on each new machine because it was in my profile. When I checked, I found out that this thing hadn't been updated in three years and was likely not compatible with my current hardware. Uninstalled it, never had problems since. So yeah, that was fun. At least I got a new laptop out of it.
Also sometimes I take responsibility for fucking up silent updates - I hear the fan spinning up but I still feel the need to reboot just to settle things down.
Not an IT, a friend onced told me their phone was getting hot and draining battery fast from last night. Naturally I asked if they installed any new apps or changed settings couple of times and the answer was clear no.
I checked the apps list and saw an obviously sus app (might be miner). I asked from when they had that app and they said 'why? I installed it last night'.
That was the kind of app you get clicking 'horny milves in your area' ads.
My mom complained that her phone drains the battery from 100 to 20 in like 5 hours. I asked if she had installed something stupid, answer was obviously a no. Checked her apps and there was some gif keyboards and emoji keyboards and at least 3 different mirror apps and all kinds of garbage...