title: Sharepoint seeking authentication when opening Word / Excel files from website
body: <p>The company I work for is using SharePoint as a CMS for it's public facing website. I recently enabled FBA (Forms Based Authentication) for the site in order to provide some user specific functionality, but this has caused a side effect with Word / Excel files when opened from the site using Office 2007 / 2010.</p>
  
  <p>Some users are challenged for authentication when opening a Word / Excel document from IE (but not when they're select "save file" instead of "open file"). A window pops up behind IE / Word / Excel (so you often don't realise it's there) showing the sites login page. If the window is dismissed then the document continues to open normally.</p>
  
  <p>It seems to be environmental. Most Office 2007 / 2010 users internally experience this and we've had one report externally of this happening.</p>
  
  <p>Anyone know how to prevent this behaviour?</p>
  
  <p>In case it's relevant: The company also has an internal SharePoint site using NTML authentication allowing internal users to edit the same content visible externally.</p>
  
  <p>I originally suspected the SharePoint header added to responses may be alerting Office to check for authentication to allow extended functionality, but I remove the response header in IIS and it didn't make any difference.</p>