Indeed this may very well be related to the sponsor program. Check out
How to uninstall ad-ware/sponsor to see how to get rid of them.
If you have already used other ways to try and remove them then it might be needed to reboot, reinstall Plus! with the sponsor, reboot, uninstall and reboot again. This because the uninstaller might have got corrupt when you used other means of removal, which did not work properly.
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