Most homes today have wireless routers that users use to connect to Internet wirelessly. Your router could have a long range and it is possible that it reaches your neighbor's home or apartment as well. Your neighbor could connect to your router and use your Internet connection if not properly secured. This can slow down your Internet speed. Fortunately, in a few easy steps you can find out if someone is using your Internet and then take appropriate action.
Open a web browser and type the IP address in the address bar.
You will see the menu page of your router. Click on a button labeled something like "DHCP client list."
On this page, If you have a password setup for changing settings, enter the password and click on a button labeled something like "Submit." If you do not have a password setup, leave the password field blank and click on a button labeled something like "Submit."
You will see a list of IP Addresses of all computers connected to your router. The number of IP Addresses is the number of computers using your Internet connection.