Windows Live OneCare 2.0 was released back in mid-November and, ever since, we haven't heard much from the Windows Live OneCare team. That should change soon, as LiveSide has noticed a 2.5 English-only public beta signup page. Hopefully the official blog entry will appear soon, since at press time a changelog was nowhere to be found. When it becomes available, though, you can expect this post to be updated accordingly.
Until then, fill out the short beta signup form (after you check your computer meets the system requirements) and click the download link that appears. Unlike previous betas, this one allows you to live in a choice of geographical locations beyond just the United States (17 countries in total). After the lengthy installation in which Windows Defender is turned off (assuming you're on Vista or you have it installed on XP), you'll be prompted to restart. The exact version number is 2.5.2744.0:
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