You need to limit access to the router by creating an SSID and a Security Key, as follows:
1. Connect the computer to the router using the Ethernet cable so that you can access the router’s set up details. This is done by typing 192.168.x.y into a browser address bar window. The values of x and y depend upon the make of router. If you don’t know the values, click the Windows Orb (Start) > Run, type cmd /k ipconfig (note the two spaces) and press Enter. Make a note of the Default Gateway address and enter it into the browser window. When asked for the username and password, type the default values for your router (see your user manual).
2. Now look for a section named wireless or similar wording and find an SSID name and a Security key. Change the SSID to something more meaningful to you but don‘t use obvious names, like your name. Also, if the key type is set to WEP, change it to the more secure WPA, unless computers with older WEP-type adapters want to connect. Now change the Security key and make a note of it and the SSID.
3. Your router may have a section that allows you to backup and restore the router configuration. If so, make a backup to enable you to easily restore the set up in the event of having to reset the router to factory settings.
4. The SSID and key are needed for any wireless computer to connect to a router. The software varies from manufacturer to manufacturer, but generally it involves right-clicking the wireless network adapter’s icon in the Notification Area (bottom right of screen) and following the prompts to create the initial connection.
So, to summarise, any computer user wanting to connect wirelessly to your router will have to know the SSID and the Key that you created in 2 above.