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CRC of MBR or UEFI boot loader changes at every restart?

Anonymous
2013-07-24T20:28:08+00:00

I have a Fujitsu Esprimo desktop running Windows 7 Professional.  Every time I restart, it stops before loading Windows with the following message:

"The CRC of the boot drive MBR or UEFI boot loader has changed since last boot.

Press any key to enter setup."

In order to continue, I have to go into BIOS setup, exit without any changes, then Windows loads normally.  This repeats at the next restart.

I have run chkdsk on the system drive (C:), and no problems were found.

What would cause this, and how can I change it?

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  1. Anonymous
    2013-07-25T21:01:29+00:00

    I've never enabled this setting on my laptop. I'm not certain exactly what it's checking - whether it's just the MBR or other things like Bootmgr and BCD. On a system with only Windows 7 installed I wouldn't expect the MBR or Bootmgr to change after installation. Did this start after an update? The Reliability Monitor may show any changes with occurred around the time this started.

    I assume the Fujitsu support have checked that you have the most up to date BIOS. Have you tried disabling the virus warning and then enabling it again in case it needs resetting? Even if it is a boot virus, I wouldn't expect it to be constantly changing so as to cause the detection at every boot. If you want to eliminate this possibility, it's best to use an offline virus scan like Windows Defender Offline. 

    An outside possibility is that Webroot is doing something clever with these files that is causing the problem.

    You can reset the MBR and Bootmgr using the method here:

    http://support.microsoft.com/kb/927392

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  1. Anonymous
    2013-07-24T20:51:52+00:00

    My Fujistsu S751 laptop has a feature for checking if the bootloader has been changed. It canbe switched off. Here is the relevant section from the S751 manual.

    Virus Warning (device-dependent)

    This field checks the boot sectors of the hard disk drive to see if any changes have been

    made since the previous system start-up. If the boot sector has been changed since the

    previous system start-up (e.g. new operating system or virus attack), a warning is displayed

    on the screen. The warning will stay on the screen until you acknowledge the changes by

    clicking on Confirmor until you set the Virus Warningfunction to Disabled.

    If the boot sectors have been changed and the reason for this is unknown, a

    programme for finding computer viruses should be loaded.

    Such a change is not only caused by viruses, but also by the boot manager.

    This function does not replace proper anti-virus software.

    No supervisor password is required to set it up.

    ► Call up the BIOS Setup and select the Securitymenu.

    ► Highlight the Virus Warningfield and press the Enter key.

    ► Select Enabledto activate the Virus Warningfunction.

    ► From the Exitmenu, choose the option Exit Saving Changes.

    ► Press the Enter key and select Yes.

     The notebook will restart and the settings will be adopted

    (the copy didn't handle the formatting properly but you can still understand it)

    Check the Esprimo manual for a similar setting.

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  2. Anonymous
    2013-07-25T14:27:52+00:00

    Thanks, dax1792.

    I need to clarify.  I was aware of the Virus Warning option in BIOS, and that disabling it would avoid the startup issue.  What I am wondering is why the CRC of the MBR would change every time I restart; or why the BIOS would report that it has changed.  I assume that this is abnormal, and I am wondering if there is some issue that needs to be addressed for the well-being of my PC.

    Also, in addition to running chkdsk, I have Webroot SecureAnywhere running continuously, including scanning the MBR, and it has not reported any problems.  Fujitsu tech support also ran SuperAntiSpyware on my system.  It detected lots of tracking cookies, and also 3 files it identified as Trojan.Agent/Gen-Frauder, but I am pretty sure those are false positives; I have reported them to SuperAntiSpyware for review.

    It is interesting that the manual for your laptop says boot sector changes can be caused by the boot manager; should that happen every time the computer is restarted?  Given that I have Webroot running continuously, is it safe to disable the Virus Warning option in BIOS?

    Thanks for your help.

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