I downloaded the 64-bit version of Kali 2016.2 as a VirtualBox VM. I successfully imported the machine into VB, and successfully did the "apt-get update" command. VB Guest Additions appear to be included in the VM when I downloaded it because it immediately went to full screen after logging in using the default username and password.

Then I decided I wanted to upgrade this version to the latest and greatest of everything.

I entered "apt-get upgrade," and it proceeded to successfully download 980+ items and install each and every one of them. I don't recall it every saying it had an issue. Here is where my problem comes in. At some point during the upgrade process, it rebooted on its own. When it rebooted, it came up to the login screen, and then I typed in the default like I normally do. This time, however, it told me I was using the wrong username and password. I know for a fact I never changed it because I never had a reason to.

The only way I can get back to using the program is to completely remove the VM from Virtual Box, delete all the files, and then re-import the VM. Then I can power it up, and log in as usual.

Is there a way I can still have the ability to have the latest and the greatest version of Kali 2016, but without having to download the ISO image and create everything from scratch? Is there an easy fix to the problem I am currently experiencing?