Slackware :: What Software For Checking On Unauthorized Network Traffic?

I have been thinking lately about the number of computers connected to the internet that become "zombies" for sending out span (or worse) when they are attacked with ssh over the internet using some kind of script. Today, I read an article in a magazine about internet detective work when you find that there has been an unauthorized attempt to connect to your machine. According to this article, almost any computer connected to the internet is attacked very frequently and the log files of that computer will show this. I have seen these in my own log files in the past.

I have learned a number of ways to track down the attacker (to a very limited degree). But what I would like to know is a relatively easy application to run and understand to monitor my network traffic and find these attempts quicker. I know I have probably almost nothing to be concerned about, but I would like to be able to head this kind of problem off. I have a number of machines connected to the net and each other and my wife does a lot of business on the internet. So, besides becoming a bot for some criminal, I don't want any credit card details stolen.I have read about Wireshard, snort, etc. Is there an application (with gui preferrably, but not mandatory), that is novice compatible that will let me monitor this?