title: MSI how to detect is Excel running
body: <p>Our application is Excel add-in. We use Wix 3.10 to build MSI. Currently we can perform uninstall of the app even if Excel running with connected add-in. <strong>I need to interrupt uninstall process if Excel is running.</strong> We don't need to close Excel, I just need to detect is it running. If so, I need to show appropriate message to user and stop uninstall process. How to detect is Excel (any app) running during uninstall process ? 
  Can I achieve desired behavior using "standard" MSI/Wix capabilities or should I write some custom action ?</p>