Someone is using my Wifi.....

We all know you have to secure your wireless network...we all know we need to use good passwords...but, how can we tell if someone, some how, managed to connect to our wireless network? got an IP and browsing the web from our wireless router?
EASY...use MyLanViewer Network Scanner / IP Scanner

The program displays your network computers in an easy to read, buddy-list style window that provides the machine names, IP addresses, MAC addresses, shared resources and other technical details for each computer.