Disable edit workbook option for view only onedrive files

Hi,

I want to limit file access for an excel document in my one drive to only allow people in my organisation to access it, and just in a read only mode. This works to a point if I select the restrict access - view only option, people need their work logins to view it and cannot edit it from One Drive. However, my colleague tested it for me and she can open the doc in her desktop excel via the Edit Workbook button, and then it is completely editable.

We need to prevent users from being able to save the information or email it on outside of our company. Does anyone have any ideas? 

Many thanks,

Christa