Is There a MBR GPT Virus/Malware Thing?

This is a completely new install of win10 I have just now put up.

The fourth this year.

The third in about the last 3 - 6 months.

I'm very slack about keeping records but the previous two I am completely sure had MBR boot partitions on UEFI computers - and that's not what they should have had and not what they were set up with when Windows was installed on them.

This very computer here had a new install put on in desparation a few months ago - maybe only two or three - and I went and bought a completely new disk for it to make sure it was a good install.

My son's computer went down last week and eventually we found that same problem. Windows tells you. You go to make a new install and it tells you it can't because it is MBR.

So for sure something is changing these boot partitions.. For sure.

Does anyone have any knowledge of what it might be? A virus? Malware?

Assuming you have gpt and secure boot secure boot won't boot if the boot files are changed by malware

Just because the computer is UEFI capable does not mean that Windows was installed in UEFI mode on a GPT drive. If CSM is enabled in UEFI firmware settings it is completely possible to boot the installation media (likely a USB flash drive) in CSM (legacy BIOS) mode. That would cause Windows to set the drive as MBR partition type, not GPT.

Windows 10 installs in the same mode the installation media was booted in.

NavyLCDR is correct. My Lenovo is UEFI capable but Windows was originally installed in legacy mode on it. I converted it to UEFI several months ago using Brink's tutorial, listed below:

Convert Windows 10 from Legacy BIOS to UEFI without Data Loss

Isn't it disturbing when your certainties get overturned? So it is not 'for sure' that they were changed from gpt to mbr.

Hmmm.

Well I'll make sure I know what my current one is for future reference. I just checked it: gpt.

:)