From time to time I see my CPU usage spike and my laptop starts to heat up.
top and see that an unrar process is running and consuming anything from 40 - 99% of CPU capacity.
I try to kill it using
sudo killall -9 unrar or similar, but the process either respawns straight away or keeps running.
I'm a reformed mac user who's only been running Ubuntu for a year, so sorry I can't provide any more detailed information.