Released to harden security and provide a more secure communication channel, a new client is rolling out for Windows computers.
There's practically nothing to do, right now, but wait for the new client to rollout through Automatic Updates. The update will be rolled out gradually and methodically, as long as Automatic Updates is turned on. The update will be made available as a separate download in the future so that it can be deployed using WSUS or another deployment mechanism like System Center Configuration Manager.
Windows 8.1, Windows RT 8.1, and 2919355 has been applied, so this is more a notification for computers and servers running Windows 7 Service Pack 1 (SP1) and Windows Server 2008 R2 SP1.R2 already includes these improvements if
Full information about the client update can be found in KB article 2887535: Update to Microsoft Update client
In the article, Microsoft states that the current client is a problem in the Microsoft products that are listed in the "Applies to" section, but doesn't go into detail about a potential security risk or unreported vulnerability in the current Microsoft Update client. This verbiage seems to indicate that a risk does exist but is not being reported at this time.