Make an existing VM immutable
Solution 1:
This works for me:
- Halt the VM if it's running.
- Open the "Storage" settings for the VM where the HDD image is attached. Detach the image.
- From the VM Virtualbox Manager window, select File->Virtual Media Manager.
- In the media manager window, select the hard drive image that you want to change.
- Select the "Modify" button, or right-click on the image and select "Modify...". Change the image to immutable and click "OK".
- Return to the storage settings for the VM and re-attach the HDD image to the VM.