The last comment of mine regarding "official xenial repository" is wrong - I installed virtualbox from the virtualbox.org provided repository.
The virtualbox package from virtualbox.org has
Recommends: [...] module-init-tools, linux-headers-generic | linux-headers-generic-pae | linux-headers-686-pae | linux-headers-amd64 | linux-headers-2.6-686 | linux-headers-2.6-amd64 | linux-headers, linux-image, gcc, make | [...]
whereas the official ubuntu 'virtualbox' packages does not recommends linux-* packages.
The last comment of mine regarding "official xenial repository" is wrong - I installed virtualbox from the virtualbox.org provided repository.
The virtualbox package from virtualbox.org has
Recommends: [...] module-init-tools, linux-headers- generic | linux-headers- generic- pae | linux-headers- 686-pae | linux-headers-amd64 | linux-headers- 2.6-686 | linux-headers- 2.6-amd64 | linux-headers, linux-image, gcc, make | [...]
whereas the official ubuntu 'virtualbox' packages does not recommends linux-* packages.