Windows Server 2008 R2 Security Guidance
What's New in Security in Windows Server 2008 R2
Windows Server 2008 R2 introduces some changes from the security perspective of the operating system. The core changes are related to: authorization and access control, identity and authentication, information protection, security policies and security roles. To see the complete list of changes see What's New for Security in Windows Server 2008 R2.
Related security focused content covering Windows Server 2008 R2 and Windows 7 :
Windows Server 2008 Security Guide
Using Windows 7 and Windows Server 2008 R2: Controlling Communication with the Internet
Threats and Countermeasures - Security Settings in Windows Server 2008 and Windows Vista