I would like to make the widget also non visible to admin and editors.
I therefore installed a the Dynamic Widget plugin
(http://wordpress.org/extend/plugins/dynamic-widgets/ ) which would allow me to hide the adsense widget for admins.
However the dynamic widget plugin used on the Quick Adsense widgets creates an error ... " WidgetID is not valid ".
I thought this might be an error from the dynamic widget plugin, but it looks like the bug is in the Quick Adsense widget for registering the widget "the old way".
Please look at this support post, where the dynamic widget author explains it in detail:
Would be great if the QA widget would work with the dynamic widget plugin, allowing to have more control over it.
Please have a look into it.