Just to keep you all in the loop, I've just received the following information from Microsoft regarding the stealth update.
In particular, I was interested in finding out whether the rumors that the stealth update was in order to correct a problem with the Windows Update mechanism. According to a Microsoft spokesperson, the update was NOT sent to users to correct a problem with Windows Update:
Q. So what had happened between the 14th and the 24th of August to break Windows Update?
A. Nothing was broken in Windows Update during this time. In order to constantly improve the performance and reliability of Windows Update, Microsoft periodically updates the Windows Update client-code automatically. Users should not be concerned that it is broken, but rather that periodic refreshes to the code help Windows Update continue to service customers.
I was also curious about why the information in the Event Log was so vague.
Q. Why is the entry in the Event Log for this update so vague?
A. We realize we weren't as transparent as we should have been, and are working to do better in the future, both in terms of entries in event logs for WU, and in terms of helping people better understand how the WU service works as a whole.
And why there was no knowledge base article relating to the update ...
Q. Why no knowledge base article?
A. It is good feedback, and it's something they are considering as they listen to customer feedback about how they can be more transparent in the future.