you still have to have a trusted mac address list to do that, which means he will still have to do what i mentioned earlier. Besides, it seems more logical to try to keep the foreign connections out in the first place than to have software to tell you about it after the fact.

That is a spiffy little application that I'm glad to now know about, but I don't think it's going to be much use to someone that seems to know little about networking. Just the fact that it is designed to work with Ethereal ought to tell you what kind of person it is designed for. ;)