When users try to launch Microsoft Office documents that reside on a non-SharePoint server an authentication or security or certificate prompt could popup behind the IE window, giving the appearance that IE has hung.
This issue affects both Office 2010 and 2013 on Windows 7.
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, the following article number to view the article in the Microsoft Knowledge Base: (http://support.microsoft.com/kb/322756)
The user can minimize the IE window to see the prompt.
In some cases setting the HKEY_CURRENT_USER\Control Panel\Desktop\ForegroundLockTimeout registry key to a value of 0 can cause this issue to go away. A possible side effect could be windows coming to the foreground that may not have jumped to the foreground before.
The product group has been informed of this issue. This blog will be updated when more information is known.