This is in regards to Microsoft Security Bulletin MS15-011 - Critical, https://technet.microsoft.com/en-us/library/security/ms15-011.aspx
This security update resolves a privately reported vulnerability in Microsoft Windows. The vulnerability could allow remote code execution if an attacker convinces a user with a domain-configured system to connect to an attacker-controlled network. An attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. This security update is rated Critical for all supported editions of Windows Server 2003, Windows Vista, Windows Server 2008, Windows 7, Windows Server 2008 R2, Windows 8, Windows Server 2012, Windows RT, Windows 8.1, Windows Server 2012 R2, and Windows RT 8.1. For more information, see the Affected Software section. The security update addresses the vulnerability by improving how domain-configured systems connect to domain controllers prior to Group Policy accepting configuration data. For more information about the vulnerability, see the Vulnerability Information section.
We urge all subscribers to update their Windows OS immediately. For clients have subscribed to managed service, our engineers are already in the midst of updating/ patching the operating system and arrange with you if reboot is required.