.NET 4.6.1 is available and is a recommended update on Windows Update. Both the Exchange team and SfB team have both recommended you do not install this update on Exchange or Lync/SfB servers.Guidance on how to block the installation of the recommended update: https://support.microsoft.com/en-us/kb/3133990
Link to the NextHop blog with this info.
Link to the Exchange team blog with Exchange info and information on how to roll back to .NET Framework 4.5.2 if 4.6.1 was already automatically installed.
