KMSOffline is a popular one-click activation tool developed by Ratiborus that emulates a Key Management Service (KMS) to activate Windows and Microsoft Office products. Preparation

Some users report that after using KMSOffline v2.4.5, Windows Update fails, or specific system files become corrupted. The tool modifies system files that are not meant to be touched (e.g., sppsvc.exe – the Software Protection Platform service).

However, even "official" KMS tools exist in a grey area; there is no Microsoft-signed version.