Windows Installer 3.1 (v2) is available at official Microsoft web site. Go here:
http://support.microsoft.com/?id=893803Few features:
New features in Windows Installer 3.1• New minor UpdateTargetRTMProperty property: Patch files can now target both the original release baseline and the latest service-pack-level baseline that is on the system.
• New MsiSetExternalUIRecord API: Packages that use an external user interface can now receive messages as records instead of receiving the messages as strings.
• New x64 and Msix64 properties: Packages can now use the x64 and Msix64 properties to indicate x64 processor-based operating system support.
• New MsiNotifySidChange API: You can use this API to upgrade the Windows Installer configuration if the security identifier (SID) of a user changes.
• Flyweight patching is now an opt-in behavior: Windows Installer 3.0 introduced new "flyweight patching" functionality. By default, this functionality was enabled for all patches. Windows Installer 3.1 now disables this functionality unless you specifically enable the functionality by setting the OptimizedInstallMode property in the MsiPatchMetaData table.
Issue that is addressed in Windows Installer 3.1 (v2) • Windows Installer no longer fails silently when the installer tries to update a file that is protected by the Windows File Protection feature.