tj03 gave kudos to Marcos in Online Scanner
We are not aware of an FP on Windows update, that should basically never happen since such files are typically trusted and our detections are smart enough not to detect clean files. When FPs happen, it's not on Microsoft's or other popular files.
You can install ESET, activate a trial license and have the disks completely scanned. You shouldn't need to format the disk and reinstall the OS.