Malware is like a cancer.. it can replicate itself into many other files, and that is part of the 'last steps' toward a total system failure.
If a viral sweep finds signatures in executable files, then those files are deleted or moved to a virus "vault" for security.
The only way to reformat a hard drive is to use the OS install disk.. then delete any existing partitions, then shut down and restart with none formed.. then create partitions as required. The security features of the OS install process prevent deletion of existing system files. Many system files have been updated by the support process.. thus the error message about being "older" than the current version. You will have to start from scratch.. and get all the updates again.
F@H.. to solve mankind's maladies.. in our lifetimes!