Hi John,
Here's another option, although I admit it requires rolling up your sleeves
a bit.
I don't know what brand of WiFi router you're using, but many allow you to
see what machines are logged on by going to the router's setup screen. Your
user guide should walk you through how to do this, but typically you punch
your router's default IP address--192.168.1.1 is a typical one--into your
web browser to access.
Then you should be able to see what machines are logged on (or have recently
logged on) by looking at the DHCP settings. It sounds intimidating, but the
concept is simple: Whenever a wireless device wants to log on to your
network, your router assigns it an IP address. If you know you have two
wireless laptops in the house, but see five assigned IP addresses, it's a
clue that you might have some freeloaders.
Each wireless device also has a unique code--called a MAC address--that you
can use to prevent this. Your router should show you all the MAC addresses
of devices within range and give you the option to filter out ones you don't
want to log on. This is a great way to beef up the security of your network.
Hope this helps. Let me know how it works out.
Michael Stroh
User Assistance Writer
Microsoft Corp.