[Picture from winsupersite.com]
As part of Microsoft's new 'Windows Live' marketing push, they are marketing a new complete security solution for Microsoft Windows XP and Windows Vista, called Windows OneCare Live. It will provide antivirus, firewall , antispyware and backup capabilites, all easily accessible to view and control from one OneCare centre. The beta is free (US only, however) and apparently gets you a discount on the product when it does finally come out.
This looks like Microsoft branching out into the (large) sphere of Windows security products out there. It looks like they will try and take on the big players like Symantec and McAfee, and are marketing OneCare Live as a separate product, as the EU would not be happy if Microsoft included it in Vista.
(On a completely different topic, there's a very complete list of all April Fool's Jokes this year here on Wikipedia).