This is default behavior. The default hidden shares on a Windows machine are each major drive letter, ADMIN$, IPC$, and some others that are specialized to certain server roles. This behavior is referred to as "Administrative Shares." Only administrators can access these shares so unless you're handing out user accounts that have admin access to each other PC on the network, you're fine. If you're logged in to a PC as a regular user, not a domain admin or a local admin that has the same username and password on the other PCs on the network, and you can still get to the admin shares, then yes, there is a problem.
It is such a base feature of Windows that disabling them can have potential downsides. Be mindful of KB842715. To disable it permanently, you will have to use a registry edit at HKeyLocal Machine\SYSTEM\CurrentControlSet\Services\LanManServer\Parameters
. On servers edit / add AutoShareServer
and make the REG_DWORD
value be 0. On workstations edit / add AutoShareWks
and make the REG_DWORD
value be 0.