The SecureCustomProperties is a list of public properties delimited by semi-colons. These properties are included with the default list of restricted public properties that the installer can pass to the server side when doing a managed installation with elevated privileges.
||Windows Installer 5.0 on Windows Server 2012, Windows 8, Windows Server 2008 R2 or Windows 7. Windows Installer 4.0 or Windows Installer 4.5 on Windows Server 2008 or Windows Vista. Windows Installer on Windows Server 2003 or Windows XP. See the Windows Installer Run-Time Requirements for information about the minimum Windows service pack that is required by a Windows Installer version.