Amid reports that Windows Live OneCare changes settings in Windows Update to allow for automatic installation of important updates, the official word from Microsoft is that this is by design. When first installing OneCare, the setup informs the user that proceeding will change computer settings to automatically download and install important updates from Microsoft Update. Settings for recommended and optional updates are not changed. Even during Tune-up, OneCare checks, and then prompts the user if there are missing software updates or if Automatic Updates settings have been changed.
"OneCare is built for people who don't want to worry about protecting and maintaining their PC. This behavior is by design and is not unique to the latest version of OneCare. It helps ensure that your computer continues to receive important updates as soon as possible after they are released. We are evaluating user feedback and will be revisiting how we communicate the installation details of Windows Live OneCare as we are continually working to improve that experience. In addition, OneCare was built with privacy in mind, and Microsoft takes that very seriously – every new feature or setting change is reviewed and approved by Microsoft's privacy experts."
News source: WLOneCare Blog