Red dot on taskbar icon after a scan

The red dot on the taskbar icon indicates newly discovered devices (the ones that have not been seen on that network before). It displays a number for up to nine devices, and a plain dot for ten or more. Clicking a device in the list clears its highlight and reduces the count.

If you would like to remove the dot, go to Options → Program Options → History and untick "Enable device history". New devices will then no longer be marked after a scan. Note: this also disables the device history itself, such as the first seen and last seen information.