Specifies a shared identifier that represents multiple versions of an application, represented by a string GUID. This property is used by Windows Installer to check for installed versions of the application during installation.
The UpgradeCode should only be set for the first version; it should never be changed for subsequent versions of the application, nor should it be changed for different language versions. Changing this property will keep the DetectNewerInstalledVersion and RemovePreviousVersions properties from working properly.
The Product Code and Package Code are different properties. To set the Product Code, see ProductCode Property. Visual Studio does not support setting the Package Code. However, you can access and modify it by using the summary information screen in Orca.exe, a table editor for creating and editing Windows Installer packages and merge modules. See Orca.exe on the MSDN Web site.