It appears that there is a very serious bug which will affect users of Windows 7 and Windows Server 2008 R2.
This vulnerability affects SMB (Windows Server Message Block) this is the part of the system which deals with Network resources such as access remote printers and access to remote computers.
Microsoft confirmed that currently there is no fix for the problem. Only one solution is to disable SMB and await for update from Microsoft.
Apparently this attack can be performed even if on the machine firewall is enabled.
more informations on author blog.
Windows Server 2008 R2 Product Overview
Windows Server 2008 R2 builds on the award-winning foundation of Windows Server 2008, expanding existing technology and adding new features to enable IT professionals to increase the reliability and flexibility of their server infrastructures. New virtualization tools, Web resources, management enhancements, and exciting Windows 7 integration help save time, reduce costs, and provide a platform for a dynamic and efficiently managed data center. Powerful tools such as Internet Information Services (IIS) version 7.5, updated Server Manager and Hyper-V platforms and Windows PowerShell version 2.0 combine to give customers greater control, increased efficiency and the ability to react to front-line business needs faster than ever before.