Some months ago I bought a desktop system. I hadn't had one for years, but a very strange and unexpected need came up; I wanted to play games with my son who lives in Greece, in an attempt to spend a bit more time with him, even virtually. I bought and built a desktop system based on AMD's excellent Ryzen line, but that's for another time. On that computer, and as it would be used predominantly for games, I installed MS Windows. That is another thing that hadn't happened in my household for decades!

Of course being who I am - and among others, not a big fan of gaming - it was not even a couple of weeks before several Linux virtual machines started popping up. Initially on Hyper-V as it was more than enough for the job, but when the need for the first VM with a graphical user interface - a Kali Linux box - came up, I switched to VirtualBox. The main (maybe the only?) reason was that Hyper-V has an annoying bug: it doesn't support bidirectional clipboard with Linux guests.

VirtualBox has come a long way since I last used it. In the end of March, a message came up when I tried to update my Kali box:

Hash sum mismatch

A security person never dismisses such a message, although I understand how this can happen if I try to update at the same time the mirror syncs the packages. That should normally be resolved in ~5 minutes, but in my case, the problem persisted.

I switched Kali repository mirrors and manually selected one that had current updates. The problem didn't go away. I started searching and trying to fix it following advice on the internet - the most common of which was to scrape the apt cache and lists. To no avail.

During this search, I found out that people /behind network filters/ were among the ones affected. And then I remembered reading about a recent Microsoft update that was messing up with the network stack. My computer didn't have network issues. It seems and still does seem to work flawlessly. But installation of a Windows patch to the host machine and a reboot, allowed my Kali virtual machine to retrieve updates without the dreadful Hash sum mismatch error message.

Coincidence? Maybe. But in any case, I now add to my troubleshooting playbook the probability that even when things seem (and should) be unaffected by the virtual network stack, I should also try to troubleshoot the host machine.