I just installed CCleaner free version 5.45 today. I disabled Monitoring in Options, but continued to see the C in the System Tray.
I then went INTO CCleaner, disabled the Startup item and rebooted.
The C did not appear upon reboot.
Is there some sort of bug with this? I saw also today that How-to Geek was recommending AGAINST using CCleaner because the monitoring seems to be forced on. I hope this is a temporary glitch and will be fixed soon.