Have you been mining for other people?
I stumbled upon a site today while looking up a tutorial. This site immediatly used 600% of my CPU (6 threads at 100%) and was making my fans go crazy.
I thought this was particularly terrible because it's a tutorial so there is a great chance that I would keep that tab open for a while.
Here is the code I saw that led me to believe there was crypto miners:
That all leaves me to believe that this site is a spam site that runs crypto miners in the background.