[ Thanks to finid
for this link. ]
“If you are reading this, you have likely attempted or actually
set up a dual-boot system between your favorite Linux distribution
and Windows. And if you did that on a computer with a single hard
drive, that is, dual-booting Windows and Linux alongside each
other, you probably replaced the Windows boot loader with GRUB, the
Linux boot loader, in the Master Boot Record (MBR).“Though that is not what I recommend, many still prefer it that
way, even as I have written in many of my dual-boot tutorials that
Windows will, during a reinstall, overwrite anything it finds in
the MBR, and that some anti-virus programs tend to write small
files to the MBR, messing up GRUB. “