I've got an old Airport Express, which looks kind of like the A/C brick and sits in a wall socket. It's got a WPA password which shouldn't be possible to guess. Today, I opened up a finder window, and I saw "Brian Severson's Computer" in the sidebar. I don't know who this person is or how they connected to my network. WPA security can be broken through, but it sounds like it takes some determination. I live in a dense area, with a handful of open, if slow, wifi points around, so I'm concerned that someone is breaking onto my network because they want to do something illegal. My question is: how do I keep them off? I've already changed the WPA password and turned on MAC address filtering. What else should I be doing? How can I know if they try again?