This isn't SP1 or beta software or even malware (perplexed9, use some common sense). It's an update that readies the system for when the service pack is released. This occured with the service packs for Vista too.
However this update should not have been released without proper documentation so it wouldn't surprise me if people hold off until there are notes available.
*UPDATE* - Documentation has been released - http://support.microsoft.com/KB/976902