Originally Posted by
PorkRind
Computers capable of using and creating CIFS file shares (Windows, Linux and, I believe, Macs) create broadcast network ("NETBIOS") packets that contain the computer name. On a conventional office or home network, every computer "sees" every other computer's name broadcasts since it's very common to share resources and there's no real need to hide them from each other.
On Windows 7 (or Vista) this is one of the reasons for the "is this network Home/Work/Public" when you connect to a new network. The first two enable firewall settings that allow those to go out and come back; the "public" setting blocks them. When in doubt, always pick "public." For those still on XP, while the Service Pack 3 firewall improvements help, it's probably still best to run a 3rd-party firewall program that blocks all of that stuff.
Linux CIFS file sharing will depend on your configuration, but most people running desktop/laptop Linux installations are likely to have the "incoming shares" service (Samba - actually in two parts, one for name management [nmbd] and one for actual file sharing [smbd]) turned off, and only the client part enabled. This will mostly be invisible on the network until you actually try to connect to someone else' system (although some other helper programs within the Gnome or KDE desktop environment may do lookups.)
No idea on Macs, but I assume it must have something equivalent to "public network" firewall settings.
The other issue with all three OSes is that machine names (etc) and personal names are now used for other broadcasty protocols to find each other's machines (see, for example, how different copies of iTunes or Windows Media Player find "____'s music library" and most OSes can now find network printers nearby) ... there is an alphabet soup of related but not fully identical or compatible protocols involved (UPnP, DLNA, Bonjour, SLP, mDNS, etc)... all of which will, in general, be blocked by "public" firewall settings under