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This might simply be a coincidence, but after the most recent batch of updates to Windows 10 my "Password on boot" option flicked off in the BIOS - though the password still exists as I needed it to access the BIOS and revert the setting back to on.

I was under the impression that the BIOS could not be altered by any operating system, am I just mistaken on that?

I am the only user of this system and have not changed that setting myself...

What - other than me and a case of short term memory loss - could have changed that setting?

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3 Answers 3

Reset to default
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Though I have never heard of it, maybe it is possible that Windows removes BIOS passwords on some devices before installing to ensure a silent install. BIOS settings can most certainly be read (and modified) by software, so this is a possibility. However, it is more likely that it simply happened as a malfunction (has happened with me before)

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  • Thanks for the answer, I didn't know software could alter BIOS settings so that's new to me, I'll probably chalk it up to a malfunction if you have also experienced it, one would hope Windows would not be built to a automatically disable security features...
    – Unencoded
    Commented Sep 18, 2016 at 19:28
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Same thing happened 4/4/2018 (m/d/yyyy) on an HP EliteDesk 705G3 SFF with Windows 10 v1703. But this is a locked down computer lab machine and its BIOS administrative password had been set.

Took awhile to figure out why it suddenly wouldn't boot because during initial setup last summer, as with all 40 new PCS in this lab, the firmware had been set to enable the Legacy (BIOS) boot and disable the Secure (UEFI) boot.

Having ruled out all the usual possibilities,
I decided to check whether the firmware had been changed. I had to use the BIOS supervisor password to access the settings and found that the settings had indeed been reset to their defaults (Disable Legacy Boot and Enable Secure Boot).

I changed them back to enable the BIOS boot and disable the UEFI boot. Then I went through the HP firmware change validation process (type in a 4 digit number to match the randomly generated number that was presented to me) and then rebooted the PC.

The PC booted into Windows 10 per normal, but then I heard the Windows startup sound!

This should not have happened because during PC setup the internal speaker had been disabled per our usual procedure to prevent random (or maybe not so random) tones and tunes from dozens of PCs from disrupting class.

I had logged into this machine several times since initial setup and it had never emitted the Windows startup or any other sound. So I restarted and again used the BIOS admin supervisor access -- discovered that the internal speaker was enabled -- disabled it and again went through the change validation process.

After booting to Windows 10, all worked normally and silently.

A check of the Windows Setup log revealed that the PC's previous shutdown was on 3/21/2018. The Setup log indicated that KB4074590 (Security Update for Microsoft Windows) was installed on 3/8/2018 (reboot did not occur until 3/16/2018).

On 3/19/2018, changes were initiated to change KB4056887 from Installed to Absent for client id CbsTask and to change KB4056890 from superseded to Absent for client id CbsTask, but apparently no reboot was necessary for these changes to occur.

Then I found "How to access UEFI Firmware settings on Windows 10/8.1" on The Windows Club website. The article showed me how to change firmware settings via Settings > Update and Security > Recovery > Advanced startup > Troubleshoot > UEFI Firmware Settings.

BOTTOM LINE: It apparently is possible for a Windows Update (or combination thereof) to override the BIOS administrator password and reset PC firmware to its defaults -- without disabling or changing BIOS password.

FOLLOW UP: After Spring semester final exams, tested the low CMOS battery hypothesis by disconnecting the machine from electrical power for three weeks. (According to the Windows event log, there had been two weeks from the 3/21/2018 shutdown until 4/4/2018 when the issue was discovered, so two weeks would be the maximum time that the machine could have been disconnected from electrical power.) However, when the machine was reconnected to electrical power and turned on after three weeks, it booted in BIOS mode per usual. Accordingly, it still seems possible that a very unusual (and unknown at this time) combination of events somehow allowed a malfunctioning Windows Update process to use Windows 10's firmware change authority to reset the firmware to its default values.

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    Thanks for the really detailed answer Bill, I'm surprised this isn't a more widely known fact as it clearly has a serious impact.
    – Unencoded
    Commented Apr 20, 2018 at 13:49
  • KB4056887 and KB4056890 are not related. One is a cumulative patch for Windows 10 1607. the other patched Adobe Flash Player. Neither of those updates would have changed the BIOS password, and I disagree, that a Windows Update even has that capability. The method you discovered to boot to Advanced Startup, is user initiated and does not bypass the password. What is more likely is, the CMOS battery is weak, and a power failure happened and the firmware defaults were applied. Neither of those updates were even released in March.
    – Ramhound
    Commented Apr 20, 2018 at 15:39
  • The recent update to version 1803 of Windows 10 erased all my BIOS settings. I was astonished to see the COMPAQ splash screen for the first time in about 11 years. The boot order for my internal hard disks had changed. CMOS battery was just replaced a couple of months ago. Such an annoying trick by the cursed Microsoft.
    – kreemoweet
    Commented Jun 1, 2018 at 3:01
  • Windows update can definitely change UEFI settings and can install firmware updates.
    – BrainSlugs83
    Commented Nov 21, 2020 at 1:35
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I have an older SSD on 0: (listed first in bios), and my bootable SSD on 1:, and I suspect that an update caused the bios reset which SSD to look at for booting.

The other day I was on the computer playing Elder Scrolls Online (awesome game) and before going to bed, shut it down, all normally. I suspect that at some point during that day, an update was applied since I have automatic updating enabled and because the next morning when I turn on my computer, after posting, it went to a bsod saying error code 0000225.

I try restarting a few times thinking it must be a glitch, but same thing keeps happening, and I'm thinking I may need to reformat or completely reset the OS. I restart again and while posting I enter the bios settings just to see if something else is wrong... and there it is... my bios has somehow been changed to look at the wrong SSD while booting.

I don't know if it'll help, but I put a pw on the bios now so maybe updates or whatever did it will now be prevented from doing so. I looked at maybe enabling the PCI Lock option in msconfig, but not sure about it yet. The big takeaway though, is that something other than me changed my bios settings.

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