Click-to-Run is a software delivery and updating mechanism available to Microsoft Office 2010. Products delivered via Click-to-Run execute in a virtual application environment on the local operating system. This means that they have private copies of their files and settings, and that any changes they make are captured in the virtual environment. Click-To-Run is fast - users can start running an application within a short time without waiting for the entire product to finish installing. Updates are carried out automatically in the background, without requiring a user to first remove an installation or install patches. Click-To-Run products are virtualized and do not conflict with other installed software.

However, because a product delivered by Click-To-Run has private copies of all its files and registration, an add-in developer cannot determine the product's existence the same way as a product that has been installed on a client computer’s hard drive. In particular, in previous scenarios where an add-in had to verify if Outlook had been installed on a client computer, starting with Microsoft Outlook 2010, the add-in should verify if Outlook has been installed, and if Outlook has been delivered as a Click-To-Run product.

Note that only 32-bit Office 2010 is supported in the Click-to-Run virtual application environment, even if the client computer runs a 64-bit operating system.

To check whether Outlook was delivered by Click-To-Run on a client computer:

  • Verify if the VirtualOutlook key exists in the following location in the Windows registry:
    HKEY_LOCAL_MACHINE\Software\Microsoft\Office\14.0\Common\InstallRoot\Virtual\VirtualOutlook
    The VirtualOutlook key is a REG_SZ value that contains the culture tag of the installed product language, such as "en-us".

For more information on delivering Office 2010 by Click-to-Run, see the Office Product development group's blog: Click-to-Run: Delivering Office in the 21st Century.