Microsoft has pulled one of the three critical patches from yesterdays Patch Tuesday, MS13-061, from further distribution. It seems that applying this update to Exchange Server 2013 results in the Content Index for mailbox databases showing as Failed and the Microsoft Exchange Search Host Controller service getting renamed. This is not good. If you have already installed MS13-061 Microsoft has published KB2879739 to show you how to fix it.
If you already installed MS13-061 on Exchange 2007 and or 2010 it looks like you should be good to go as the issue does not seem to occur with those versions.
Seeing as this is a critical update and that could result in remote code execution and that the patch has already been made available, even if for a short time, you have to assume that the bad guys are actively working on exploit code for this issue. So what should you do? Microsoft thankfully included a workaround in the original Security Bulletin for this problem, which could help mitigate things until Microsoft can reissue the patch. It involves issuing some PowerShell commands on the server and are detailed in the Security Bulletin.