WEP or WPA2 encryption has to be activated on the router under the WiFi (Wireless LAN) settings which you might access via your browser by entering 192.168.0.1 or 192.168.1.1 or 192.168.2.1 into the address bar.
I don't know what an smc router is, so I can't give you more details on that.
Don't you have some kind of manual in print or as text on the CD that might have come with the router, that gives instructions on how to properly set up your router so no one can piggyback on your internet connection?
If you set everything up you just have to connect to that now protected W-LAN and enter the chosen password.