NetBios share

Ok, NetBios is the protocol that Windows File & Print Sharing uses (it rides over TCP/IP).
When you can view the shared folders on another Windows machine, or print to a shared printer, then you are using NetBios.
All Windows machines can talk NetBios by default (even XP). There is a service on NT/2K/XP machines called the WORKSTATION service. It is this service that must run in order for a machine to receive and send NetBios info.
On a port (Transport layer of OSI) level, NetBios uses several ports: 139 TCP, 137 & 138 UDP. So, if you do a port scan against you machine and you see ports 139, then NetBios must be enabled on your machine.
When you work with Windows, you might have heard of the Interprocess Communication share (IPC$). This is the primary NetBios share on a Windows machine. It is this share that authentication takes place, using NetBios. For example, when you log into a domain workstation member, your credentials would be sent to the IPC$ on a Domain Controller for authentication.
NetBios can be hacked and attacked very easily. There are hundreds of tools that can do this. NetBios is also hated by many people, due to is prevalence (again, since all Windows machines have this on by default); go to the grc.com web site for more into on why NetBios is bad for a machine on the Internet.

hope this helps

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