KMS (Key Management Service) activation is a method used to activate Microsoft products, including Office 2021, on a network. It's primarily designed for organizations with multiple users and devices. KMS activation requires a KMS host, which is typically a server on the organization's network, to manage the activation process.

Many modern KMS activators request access to your Microsoft account or OneDrive. Attackers use this to delete cloud backups, steal personal files, or lock you out of your own email.

Key Management Service (KMS) is a legitimate Microsoft technology used for the automated activation of volume-licensed editions of software, including Microsoft Office 2021