\\MyComputer\c$
This represents the administrative share for the "C" drive on the computer "MyComputer". This works just as well for any other local drive on the computer, e.g. \\MyComputer\d$, \\MyComputer\e$ (assuming those are local drives and not removable drives).
\\MyComputer\ADMIN$
This represents the administrative share for the %SYSTEMROOT% object on the computer "MyComputer".
How to hide
The administrative shares can be deleted by a user with Administrators membership but the administrative shares will be recreated automatically at the next reboot.[1]
The following registry configuration change e.g. using Regedit can completely hide all administrative shares. If the setting is not present then you must create it.
Servers
Windows NT 4.0 Server, Windows 2000 Server, Windows Server 2003 [2]
Hive: HKEY_LOCAL_MACHINE
Key: SYSTEM\CurrentControlSet\Services\LanManServer\Parameters
Name: AutoShareServer
Data Type: REG_DWORD
Value: 0
Clients
Windows NT 4.0 Workstation, Windows 2000 Professional, Windows XP, Windows 7
Hive: HKEY_LOCAL_MACHINE
Key: SYSTEM\CurrentControlSet\Services\LanManServer\Parameters
Name: AutoShareWks
Data Type: REG_DWORD
Value: 0
