teach me more about computer security
This whole site is designed for just that... Look around, and, in the words of the Witches in Macbeth:

1 Witch: Speak!
2 Witch: Demand!
3 Witch: We'll answer!

But before you ask, search Google and search the forums for past posts asking the same/similar thing.

By the way, NetBIOS is port 139, and can be used if File & Printer sharing is enabled (as is default on Windows) for numerous exploits, and if any drives are shared you can browse files from remote computers. There's also the infamous WinNuke which uses Port 139. As I said, Google can tell you everything you could possibly want to know, and usually a hell of a lot more you didn't want to know!