MAC filtering enabled and BLOCKED device is still able to connect through my network !!!!!?

Instead of MAC blocking, do the opposite, just enable the MAC addresses of your computers at home. That will block everything else. As for blocking only, all he has to do is try to spoof another, totally new MAC address with some software, and he will get in again. Also, check the router's firmware, there may be updates to fix certain bugs....

You must not have done it correctly. Go back over it a few times and try to find your mistake. Alternatively, you can do the complete opposite. Block everybody, and then allow only certain MAC addresses, including your PC and Xbox.

Make sure there aren't any typos and you might need to reboot the router for the change to take place. You are positive once you block it he is not going back in and unblocking it? But in all honesty your netowrok should not drop when someone joins...that is really odd.

That's just plain weird. 1) Your connections should not be dropping whenever he connects to your WiFi network. Only thing I can think of, is that perhaps he's using the same IP address as your computer is. To check this out, wait until you're sure he's on your WiFi and then take a look at your Router's status pages to see what clients are connected. Somewhere, it should show the IP addresses it's given out via DHCP, and probably, the MAC address of the machine that it gave each address to. It could also be possible that he's not using DHCP at all - he just gave himself some address that he knows works on your WiFi, and it just happens to be the same as what you're using. Of course I could be completely off and his/your addresses could be completely unrelated to this problem; I'm just guessing here. 2) If you've enabled blocking, AND he's in the blocked list, AND you definitely put the right mac-address into the blocked list, AND he's still showing up in your router's status page as a connected WiFi client, AND this is all after you've rebooted your router - then there's something bizarre going on with your router. It's a relatively trivial operation to spoof a MAC address (e.g. hide your computer's real MAC address and use something else instead), but normally if this were going on then the spoofed MAC is what would should up in your router's status page. So again, double and triple-check that blocking is active, and check which MAC address he's using against your blocked list, and also against the status page. While you're at it, read up on the proper format of MAC addresses for your router. sometimes they want the numbers separated by a colon; sometimes by a dash, and sometimes just one big long string without a separator. If you put his MAC into your blocked list with colons, and it wants dashes, that could certainly explain what's going on. If none of that works, definitely give Rute's excellent suggestion a try. Actually, if you want to get serious about limiting access onto your WiFi, blocking everybody except known friends is generally better than allowing everyone except specific blocked MAC addresses anyway. Cheers; Wire