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Dual Boot

Occasional Contributor

Hello, I have used a dual boot system for years, currently both Windows 10.  One system  got infected with a virus I can't remove.  In the old days, I would install the second operating system from within the first operating system. I have extracted the installer and have it on the desktop. Can I run it to do a clean ("custom") install to the second hard drive, overwriting the system with a virus, and keeping my dual boot system intact?

10 Replies

@gordoncanada you could open setup from the operating system which is working and then format the drives with infected operating system and install Windows on it. You may also try run reset on the infected system so it is like do clean install on that system.


However, I am curious about the virus, normally we could remove all malwares and if it is undetected malware, you could submit sample to Microsoft for investigation. It is always good idea to do some investigation on malware and submit samples of it , before format the system.


Thanks for your reply. I just tried booting into the infected operating system and it won't even complete the boot process anymore. The damage done by the virus, which I wrote down but can't find, something like CLdownloader!74, grows worse all the time. I'm afraid it may make the whole system unstable if I try to boot into it again. Should I delete the OS entry using Easy BCD before formatting the infected hard drive?

Hello @gordoncanada,


I recommend you to boot using the installation media, and opt for clean install on second drive. When you're asked selecting a hard drive, format the drive first and continue with installation. 


The dual boot may remain as it is, with above step.



@Kapil Arya 

Thanks for your replies. I will opt for a clean install. Thanks for reassuring me that my dual boot system will still work.


Glad to help!

@gordoncanada you may boot into the system which is clean and update Windows Defender and right click on the infected partition and run scan on it.

You may use bootable Windows 10 installer and perform installation and in the setup select repair on the system which has problem or try format and reinstall Windows on it. However, during installation make sure you select the correct partition to avoid removing the working Windows.


Thanks everyone. I was able to install Windows 10 and maintain  my dual boot system. I'm not sure why, but I only have a legacy black and white boot  menu rather than the colourful boot menu usually associated with Windows 10 (this happened when I upgraded to Windows 10 from Windows 7 years ago), but hey nothing's perfect.

Thanks again, Gord


What is your default boot? Windows 7 or Windows 10?

In case you are seeing black and white boot selection, it means Windows 7 is managing the boot menu.


Thanks for your reply. It makes sense that there is some remnant of Windows 7 because originally I upgraded from that OS to Windows 10. Funny how the fresh install of  Windows 10 did not overwrite whatever those remnants are. Is there a way to?

Thanks, Gord

@gordoncanada I guess you didn't upgrade Windows 7 to Windows 10 and instead install it on different partition.

You may boot into Windows 10 and browse into your Windows 7 folder and copy everything into Windows 10 or boot into Windows 7 and backup your data.

Then in Windows 10, format the driver containing Windows 7 and if you restart, you would have only Windows 10.

Just make sure backup everything before formatting.