McAfee Security Scan is additional option when installing Adobe flash. Ultimately when installing Adobe flash you would want to deselect the option to install the McAfee Security Scan. This particular product is designed for consumer use, so we do not have silent installation information for this product available in corporate support. The information that I have found on this references the uninstall via the program group. I have been advised that you can contact consumer McAfee support to see if they might have some additional information on silent uninstall options.
Information provided is accurate.
McAfee Security Scan uses the Nullsoft Installer NSIS 2.22 as installer. Therefore you can apply /S to the UninstallString defined in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\McAfee Security Scan
Therefore "C:\Program Files\McAfee Security Scan\uninstall.exe" /S should do the trick.
Note that /S is case sensitive.
By the way: http://unattended.sourceforge.net/installers.php provides a good list of installer products widely used and describes some of their parameters.