For the TG862, here's a link for two documents:
http://arris.force.com/consumers/art...B-S-User-Guide . Starting on page 22 of the User Guide there is a discussion about WiFi and security. On page 24 there is a section about using MAC addresses to help secure your wireless network.
Using the MAC address filtering is one way of helping to secure your wireless network. It is perhaps the best way. When you use this facility, you basically are telling the router to only let devices which have those specific MAC addresses to use your WiFi. If a wireless device tries to access/use your network and it is not in that list, it will not allow the device to use the network.
But, it does require more work to use that protection. Sorry, nothing's free. To be able to set up and use MAC address filtering, you need to know the MAC address for ALL devices which will use your network. That will mean any occasional user such as relatives which might visit only every so often.
Once you have the MAC address, you add it to a list in the router. These devices and the people using them then become trusted.
And if you decide to go this route, it is best to record the information someplace handy. This is just in case something happens which results in the gateway (the TG862) being reset and then the list will need to be recreated.