If you suspect that someone is leeching your wireless connection, there are several ways in which you can check. On method is to view the IP addresses connected to your router. To do this, click on your Start menu, then select "Run." Type “cmd” in the Run box, then hit "Enter." Once a new window pops up, type “ipconfig” and press "Enter" again. This will bring up a list of IP addresses using your router. You can count the number of IP addresses listed compared with the number of computers that should be connected to your router to determine whether there are any extras.
You can also see the MAC addresses, or media access control addresses, of all computers connected to your network. To do so, open your Start menu and select Run. In the box that pops up, type “cmd,” then press Enter. After you have the new window open, type in “ipconfig /all” and press Enter. In the window, the column reading Physical Address is what lists MAC addresses.
Checking your firewall logs can help you see if people are intruding upon your internet connection as well. To check, open your firewall program and search for the logs. When looking at the logs, see if there is any unusual activity going on. Sometimes, you can see if a certain IP address is repeatedly trying to access your connection.