I previously downloaded the beta version of Windows Live OneCare, but did not purchase it. Does the beta version still work?
Existing beta users will still be able to use the OneCare service with the latest updates and virus definitions for several months, but you will eventually need to transfer to the paid subscription service in order to maintain the service updates.

Why does Windows Live OneCare require me to have a Windows Live ID?
As a subscription service, OneCare needs a way to identify you and allow you to access information contained in your account. OneCare uses your Windows Live ID for this purpose. You can also use your Windows Live ID as your sign-in for other Windows Live services.