It is not a system message?
If it is something you see in your browser, then you need to shut down your browser and don\'t return to that site, as it is trying to trick you.
There is a chance that other people are stealing your wifi access.
http://www.makayama.com/easywifiradar.html
Has a tool to help locate wifi access points wherever you are. It may be you and a neighbor have similar wifi routers and are connecting to each other.
You can force your router to giving you the only access, but you need your wifi card MAC address, and to edit the router setting to allow only it, and to make the IP range available small and set your computer to force the IP you are trying to connect with it.
I would suggest trying this first.
Disconnect your router from the internet so you become a standalone network.
Go into your router settings.
Check the connections (DHCP or whatever area it shows what computers are connected)
Make sure the name of your computer is the only one, and right down the MAC addres of any others, and find the area to ban those other MAC addres from connecting so people aren\'t stealing your wifi.
Also look into setting up the security on it where you need an access key to connect to your wifi.