Hacked OS X?

I was hoping someone could answer a few questions for me about network traffic and having unwanted people access your computer. The other day I was using my computer and the program 'little snitch' asked for permission for bash to connect to something like undernet.org.nl and then again for something like undernet.or.dk that looked very suspicious. I didn't allow the connections but would have normally because I assumed that bash is something trustworthy. I did a quick google and the address was related to IRC (which I also don't understand). I happened to speak with the IT guys at the university over some drinks at the bar and mentioned it and they said that they have been having a terrible time with someone who has gotten into the network from the netherlands. I thought my software firewall was on but was in fact turned off (probably my mistake). So I am trying now to learn more and inform myself but do not know where to start. I can look at the established connections using netstat but can't decipher what they are. And my ipfw.log has constant traffic (nearly every second) from addresses within our network '35000 Deny UDP 129.81.... Is that normal? Or am I becoming a hypocondriac?