It has me wondering because it keeps being randomly created at the end of ccleaner.ini, and then removed by CCleaner - as if it were trying to hide from the user.
Screenshot example from the end of my ccleaner.ini file:
I already thought it was GUID related, however I'll wait for an official response, that is if they respond. It only started doing that recently with the current v5.38, I never noticed it with previous versions.
It is indeed a GUID. It is used to associate telemetry with a particular installation of the application. It helps give us insight into all sorts of things we want to improve, such as the update and installation process. It's not hidden, so you can do what you want with it. You can read our Privacy Policy here: https://www.ccleaner.com/about/privacy-policy.
Thank you for the official clarification. In my case the update and installation process won't submit anything useful since I only use the portable build.