Downloaded a sketchy copy of some hard to find software some years ago. Once I tried to run it, I immediately noticed that the fans started spinning fast and everything was much slower. A quick ctrl + shift + esc and I saw that CPU usage was over 90% - Checking the detailed processes, I found the executable I tried to run and force-stopped it. It almost immediately restarted itself. Obviously, it already set up some other process to check for that process, so I started killing other processes with unfamiliar names until said process stopped restarting.
All good thus far, I went to check %appdata% and of course, there was a sketchy executable there that ran the keepalive process. Deleted it, searched all over for similarly named executables, everything seemed clear. Turned off the internet, rebooted the PC. Turned the internet back on and everything was still fine. I did notice later that I suffered some damage in the form of some files getting encrypted, which was why the CPU usage shot up in the first place - it was one of those ransomware type that, once finished, would no doubt sell the encryption password for a bitcoin deposit.
My other experience with malware was on Android. It’s amazing the lengths some FUCKING HARDWARE VENDORS will go in order to install adware on everything, right, Xiaomi, Samsung? Seriously, being forced to see an ad when you just want to use the fucking calculator? Fuck that shit.