WNR2000v2 Wireless Intruders?

[Computer_User1]

I have a WNR2000v2 router. Just last night I've upgraded the firmware from 1.0.0.40_32.0.54NA to the latest 1.2.0.4_35.0.57NA. The update went successfully, and I noticed a few new features, such as the new IPv6 section, excellent.

Now, here is the problem. When I went to check my Attached Devices, I've noticed the new description "(Wireless intruders also show up here)" under Wireless Devices. At first, I saw only two devices, which I recognized by their MACs as my own PCs. After a click on the Refresh button, suddenly 3 more items showed up: with IPs I didn't recognize and outside my LAN's subnet; with MAC addresses I didn't recognize either; and with what seemed like programming codes showing up in the Device Name column.

I said to myself, uh oh, may be someone was trying to intrude my wireless network. So I immediately turn off the wireless radio on the router and continued networking in wire only. Obviously, that cleared all the wireless devices. After a while, I decided to turn the wireless back on for a test, so I did. At first, the wireless devices were just my two PCs. Not long later, the strange devices came back, this time with 5 items, with IPs and MACs differ from last time, and also with codes in the Device Name column. I then went for some reverse lookups for the strange IPs and MACs, but none of them came up as valid addresses.

Since then, I left my wireless radio off. Just a little background information before I continue to my questions. First, I am an IT professional, though networking is not really my field of trade, I am fairly knowledgeable regarding computer technology. Secondly, my wireless network employed WPA2 encryption, AP Isolation and MAC filtering, plus I've disabled the WPS Pin feature on the router to prevent intrusion vulnerability.

Now my questions:
1. I would like to ask Netgear, what exactly do you mean by "wireless intruders also show up here"? Is there more documentation on this feature?

2. Also what exactly can we do, if we see what seems to be intruders? As far as I know the Attached Devices section is read only, and we can't manually disable unwanted devices.

3. Is there anyone here ever experienced wireless intrusions, even with WPA2, AP Isolation, MAC filtering and WPS disabled?