If you have a wireless-enabled computer, phone or other electronic device, you likely have used another open wireless connection at some point--such as at coffee shops that offer free wireless to their customers through an open network. When people do not put password protection on their wireless network, it is open to anyone within range. If you suspect someone is hacking your wireless signal without your permission, you should look into the matter. Stealing someone else's Internet is illegal, and can breach your computer's security. To find out who's been using your Internet, you can check the logs for foreign IP addresses.
Determine your own IP address, so you know what address is yours and what address is that of a stranger stealing your Internet connection. To find out your IP address, select the "Start" button and then search for "Run" in the search box. Open the "Run" application.
Type in "cmd" then press the "OK" button. Type in "ipconfig" when the program opens and hit "Enter." Make note of the number besides "IPv4 Address." This is your own IP address and if your wireless is secure, there should be no foreign addresses in your log.
Enter the IP address of your router into your Internet browser window and hit "Enter." The IP address of your router is located in the same place you found your IP address, beside the heading "Default Gateway."
Log into your router using your username and password. You will either use the name and password set as default, or your current wireless name and password. This will bring you into the configuration page for your specific router.
Look for an "Administration tab" -- all routers will be different, so look for similar settings for your device. Open the "Log" to view the IP addresses that are logging into your Internet.
Check the log for any instances where strange IP addresses are logging in. If your log was turned off, enable it so it will track all incoming IP addresses.
If you don't know the default user name and password for your router, look in the instructions that came with the router or go to the manufacturer's website to find it.