I have the oldest computer at my company and I use XP on it. I pretty much never get viruses or malware infections. I think once three years ago I had one that I quickly got rid of. Everyone else who has constant problems in that department is on Windows 7 or 8, and the same users have the issue over and over again.
The main factor in security is not which version of Windows, but the behavior of the users. The ones who are going to non-work related websites, downloading software they don’t need, trying to find free music or movies, opening every email attachment or clicking every link without thinking about it. They are the biggest “security hole” of all, and if it were up to me, I’d fire them the third time they had to come to me to get their computer fixed.
I am not sure you are aware of it, but there is a method available that might help you with quickly restoring or replacing a corrupted OS.
Do a search for System Rescue CD (I prefer ixquick, more privacy available than the goog) which has several rescue programs included that I have found to be quite handy over the years.
It is a bootable CD, and yes it is a Linux CD but you will only need to boot from it with no need to install on the targeted machine. Boot to the GUI option, wait about 40 seconds for it to load (depending upon the speed of your machine) and on the menubar you will find a program called “partimage” that will take a snapshot of your currently installed and functionable OS and save it to a drive of your choice.
You wil need to know or learn a few things first such as how to mount a drive in the ‘nix environment and which partition or drive your OS is located but after that you can save it to replace later if the OS becomes unusable. You can even clone it on identical machines if you need to.
Give it a try. :)