NetBus

What exactly is NetBus? I just scanned a friends network and saw this:'

Port State Service
======================
tcp/12345 filtered NetBus
tcp/12346 filtered NetBus

What does NetBus do? I have only heard of it in connection to the NetBus trojan. Any clues would be of big help. Thanks

Netbus is a remote control trojan. It allows you to remotely control a machine to the point of even shutting it off. It consists of two portions: client and server. If you do a search through google you will find more info and probably it.

Is it a legitimate program or is it only a trojan used for penetration purposes?

It was meant I believe as a trojan and has recently been attempted to turn into a legit program. If you look at earlier version you see a simplier interface. The newer version I understand is more glitter.

it can be used both ways

You must have the computer you want to infect run a .exe then when you find out their ip and whether or not they are online, you can use the other half of the proggie to control the infected comp. Make it do all kinds of stuff, nowadays, netbus is widely known, and any half decent anti-virus proggie should get rid of it, if you are infected.

With the port scan that I did it showed that the state of the port was filtered. What does this mean? Perhaps the sysadmin. is using it for his own reasons and
he has set up a packet filtering rule only allowing connections from his own PC(?)

I could be wrong, but I think back orifice came first.. and it was said to be a "remote administration tool." Which is what it does, however, it's also easily considered a trojan with a GUI. It's way too well known, was kind of cool for a few weeks in highschool when it came out.

No clue, some sys admins are partially insane.