What you should have done is do more research before taking this drastic measure. You also should have followed the instructions given on this link READ ME Before Posting A Request For Assistance!
and done those scans and a couple of the online scans to be certain that this was NOT a virus AND clean up the computer in the process. It is never a recommendation to take these types of drastic steps before ruling out everything else. Many times files will be changed because of a hotfix or some sort of update, this would be considered normal in most cases. Certainly there are instances where a virus or some sort of "invader" can change vital files BUT in those cases the user normally would notice OTHER symptoms of infection also.