"When you buy a new computer, most of the time the
operating system comes pre-installed. This is generally, unless
otherwise specified, microsoft windows. I am not considering Apple
hardware because they do not want to give you a choice. With pc's
you do have a choice although the average computer users does not
yet realise this.
"Due to the average computer users computing habits, the
pre-installed operating systems become corrupted, virus ridden or
part of a growing club of the botnet variety. At that time about
the only sure fire way of cleaning up the computer is to do a
complete wipe and re-installation of the operating system.
"This is such a common occurrence for windows users that, where
I live at least, most computer shops offer a windows
re-installation service for around $20US. This is a good little
money spinner and unfortunately people who regularly use this
service end up paying much more than they originally paid for the
license to use windows."