To further add to the information already given in this post, NetBIOS is huge security hole if not set up properly. If misconfigured, a machine running NetBIOS can leave itself wide open to anyone on the outside, giving full access to the drives on the exposed machine - I also view exploiting NetBIOS as one of the easiest 'hacks' anyone could do because of it's simplicity and how many users machines are exposed without their knowledge. Now I won't mention how these exploits work, but I will mention that some possible methods to help discourage this exploit are: passwording any shared drives or folders on your machine, running a hardware/software firewall that blocks access to port 139 from the outside, or turning off File sharing if a computer is not on a network.

Hope this helps...