But at least with a DVD you have the actual physical copy of what was installed, and you can examine it forensically after the fact, and you may even be able to

But at least with a DVD you have the actual physical copy of what was installed, and you can examine it forensically after the fact, and you may even be able to use it as evidence of wrongdoing. You can't do that with some random file that you downloaded at some point in time (this, incidentally, is why in-browser crypto is hopelessly and forever broken).