To do a bulk deactivation of users:
1. Go to advanced administration
2. Go to the model "BulkUserDeactivate"
3. Click the button "+ Add bulk user deactivate"
4. In the field "CSV File", upload a CSV file with just one column that contains the list of usernames to deactivate and click the button "Save" in the lower right corner.
5. The time taken to deactivate users may take up to 1 hour.