If you have used a Microsoft Office activator, it is advisable to take several steps to secure your system. First, uninstall the activator software and any other suspicious programs. Run a thorough antivirus scan to check for and remove any malware that may have been installed. Next, obtain a legitimate copy of Microsoft Office by purchasing a license or using a free, authorized version. This will ensure that you receive proper updates, support, and security for your software. Lastly, consider backing up your important data regularly to avoid potential data loss in the future.