High computer CPU

I keep getting a window alert from Norton anti-virus that FSX is using high CPU. They include a graph showing the usage ( at least, I think that's what it shows). They don't explain what this means. Can anyone advise?
Flight Simulator and other chat
https://forums.simviation.com/phpBB3/
https://forums.simviation.com/phpBB3/viewtopic.php?f=9&t=27537