If your network has been compromised (see my comments below) than a MAC address may well be spoofed and useless, however:
According to http://standards.ieee.org/regauth/oui/index.shtml
the MAC is from Apple... You didn't say if you're an Apple user, so that may or may not be very helpful.
00-21-E9 (hex) Apple, Inc
0021E9 (base 16) Apple, Inc
1 Infinite Loop
Cupertino CA 95014
This could also be some sort of plug and play type activity... Apple has "bonjour"... did someone get some iPhone or iPod with wireless recently?
The fact that you have a private IP address in a different range (a Class A 10.x.x.x address as opposed to the 192.168.x.x Class C you're using) is pretty suspect... that address should not be routed in your network, but no doubt it will because a lot of home equipment is designed so things just work, even when they don't make much sense. (Ease of use trumps security.)
You didn't give enough details about your setup, but I'm guessing you have wireless in your network... and I am guessing that some device you don't own has found a way into your network... and I'm guessing its not a good thing...
Make sure you're not using WEP as its so weak as to be useless... You should be using WPA2 (or at least WPA) (and if you're a Windows user, you may need to search the MS knowledge base for necessary hotfixes for WPA2/WPA). Once you switch to WPA2/WPA you still need a good strong (i.e. random) password, try generating one here: https://www.grc.com/passwords.htm
. Make sure you've set/changed the administrative password on your router, and ideally you should lock your router down so that it cannot be accessed from outside of your network (preferably it should only be accessible from a device wired into your network, not configurable by a wireless connection.)