Please refer to this article:
http://technet.microsoft.com/en-us/library/dd772681(WS.10).aspx
Windows Explorer enables access-based enumeration on shared folders by default
On a computer that is running Windows Server 2008, access-based enumeration is enabled by default on every folder that is shared by using the
File Sharing feature. (This is the default sharing feature that is available through Windows Explorer).
However, access-based enumeration is not enabled by default on the following types of shared folders:
- Shared folders that are created with Share and Storage Management, Advanced Sharing in Windows Explorer, or the net share command
- Volumes
- Folders or volumes that are shared for administrative purposes, such as C$ and ADMIN$