A couple of days ago VMware quietly released Update 1 of its management platform for vSphere, vCenter Server 5.5.
This release, unlike 5.5.0.b released in december 2013, aside several resolved issues, introduces also some new features such vCloud Hybrid Service vSphere Client Plug-in availability in vSphere Web Client and vCenter Server support on Windows Server 2012 R2.
Among the fixed bugs is reported a NTP (Network Time Protocol) daemon issue that left vCenter Server Virtual Appliances exposed to DoS amplification attack if configured with NTP time synchronization.
Here you can find the release notes and the download.