No, using KMS Activator is generally not legal. It involves bypassing the official activation process set by Microsoft for its products, which is a violation of their licensing terms. Microsoft requires users to purchase a legitimate license to use their software legally. While KMS Activator might offer a temporary solution, it can lead to legal consequences and potential issues with system security. For a compliant and secure solution, it is recommended to obtain a genuine license from Microsoft or an authorized reseller.