A: Microsoft provides a Group Policy Object (GPO) setting to hide certain drive letters from My Computer and the Windows Explorer. Hide these specified drives in My Computer is located in the User Configuration, Administrative Templates, Windows Components, Windows Explorer GPO container. The setting also affects the drive letters that appear in the standard Windows Open dialog box.
To use this setting, navigate to the above GPO container in the Group Policy Editor MMC snap-in (gpedit.msc), open the setting, and select the Enabled radio button. In the dropdown box, you can then select what specific drive or combination of drives you want to hide.
This setting only removes the drive icons from Windows Explorer, My Computer, and Windows Open dialog boxes. Users can still gain access to the contents of the hidden drives using other methods, such as typing the path to a directory on the drive in the Map Network Drive dialog box, using the Run dialog box, or using a command window. This setting also doesn't prevent users from using programs to access these drives or their contents, and doesn't prevent users from using the Disk Management snap-in to view and change drive characteristics.
More information on this setting can be found in this Microsoft Knowledge Base article. This article also explains how you can modify the GPO administrative template files (*.adm) to display your custom list of drives or collection of drives in the dropdown box of the above GPO setting.
A related setting located in the same GPO container is Prevent access to drives from My Computer. This setting can prevent users from using My Computer to access the content of selected drives. If you enable this setting, users can still browse the directory structure of the selected drives in My Computer or Windows Explorer, but they can't open folders and access the contents of the drives. Also, they can't use the Run dialog box or the Map Network Drive dialog box to view the directories on the drives.