You may receive the following warning dialog box when opening a workbook using Excel Services in SharePoint:
Be careful. This workbook contains one or more queries that might be unsafe. Do you want to enable these queries?
To suppress this and other warnings from Excel Services, go to SharePoint Central Administration > Application Management > Service Applications > Manage service applications > Excel Services application > Trusted File Locations and click on the Address that contains the workbook.
In the External Data section, under Warn on Refresh, uncheck Refresh warning enabled and click OK.
Users who access the workbook will no longer be presented with a warning dialog box.
Thanks for that, but how to do this in Office365? I'm constantly warned about external data refresh, but can't turn it off - is there a way?
I too would like to know how to turn this off in SharePoint Online/Office365.