Most users assume this error indicates a corrupt download. While that is one possibility, it is rarely the root cause. 3uTools employs a multi-layered validation routine that most Windows installers skip entirely.
This works because the validation failure sometimes occurs only on the outer stub installer. The inner MSI may install without issue. 3utools installation package validation failed
Ensure iTunes is updated, as 3uTools relies on Apple's drivers to communicate with the device. If the validation fails while downloading firmware: Most users assume this error indicates a corrupt download