Update 4/16/2014: Please refer to the following updates posted in the blog posts below released on April 16th, 2014:
Also be advised there following KB articles have been updated:
Windows Update Client does not scan against WSUS 3.0 SP2 if HTTPS is configured and TLS 1.2 is not enabled
Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2 Update: April 2014
Microsoft has been listening to customer feedback. Much of this feedback has been received and some of the results are being given back to our users of Windows 8.1 in the form of updates. Recently, a very big update for Windows 8.1 was released. Read all about it here:
Since Microsoft wants to ensure that customers benefit from the best support and servicing experience and to coordinate and simplify servicing across both Windows Server 2012 R2, Windows 8.1 RT and Windows 8.1, this update will be considered a new servicing/support baseline. What this means is those users who have elected to install updates manually will have 30 days to install Windows 8.1 Update on Windows 8.1 devices; after this 30-day window - and beginning with the May Patch Tuesday, Windows 8.1 user's devices without the update installed will no longer receive security updates.
This means that Windows 8.1 users - starting patch Tuesday in May 2014 and beyond - will require this update to be installed. If the Windows 8.1 Update is not installed, those newer updates will be considered “not applicable.”
More detailed information can be found in the following links:
KB2919355 (Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2 Update April, 2014)
A servicing stack update is available for Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2: March 2014
What's New in the Windows 8.1 Update
Windows 8.1 Update: The IT Pro Perspective
Windows Server 2012 R2 Update is now available to subscribers
For those users who are still using Windows 8 and Windows 2012 (and not Windows 8.1 and Windows 2012 R2) you are unaffected and will continue to receive updates as normal.
The new baseline only exists for Windows 8.1 and Windows Server 2012 R2.
Another important item for our enterprise users and IT pros out there: There is also an issue regarding Windows 8.1 Update preventing interaction with WSUS 3.2 over SSL connections. This has been outlined in the following blog post:
Windows 8.1 Update (KB 2919355) prevents interaction with WSUS 3.2 over SSL
Microsoft plans to issue an update as soon as possible that will correct the issue and restore the proper behavior for Windows 8.1 Update KB 2919355 scanning against all supported WSUS configurations. Until that time, we are delaying the distribution of the Windows 8.1 Update KB 2919355 to WSUS servers.
You may still obtain the Windows 8.1 Update (KB 2919355) from the Windows Update Catalog or MSDN. However, we recommend that you suspend deployment of this update in your organization until we release the update that resolves this issue.
You may also find the workarounds discussed in this article to be useful for testing this Windows 8.1 Update for your organization. Thank you for your patience during this time.
In addition, some training and readiness docs have been recently published along with updated toolkits:
Windows 8.1 Update User Readiness Toolkit
Windows 8.1 Update Power User Guide for Business
Windows 8.1 Update how-to videos for business users
Windows Driver Kit 8.1 Update 1
Windows Assessment and Deployment Kit (Windows ADK) for Windows 8.1 Update