Peter,

McAfee Security Scan Plus often gets installed as part of a bundle with free software.  This is why I strongly recommend Unchecky to all of my clients and those who are blind or visually-impaired in particular.

McAfee Security Scan Plus should definitely show up in the programs list of "Programs and Features" under Control Panel and allow uninstallation from there.
--
Brian

A great many people think they are thinking when they are merely rearranging their prejudices.

         ~ William James