If you run the free version of the popular temporary file cleaner and system tool
CCleaner for Windows, you may have noticed that it has started to display advertising popups on the system.
I noticed the behavior after installing CCleaner 5.44 on a Windows 10 Pro system; it is possible, however, that older versions of CCleaner display the advertisement as well.
The advertisement appears as a popup message in the lower right corner of the screen. It highlights a Summer Sale and a discount for CCleaner Professional.