Are "Shared" computers in the Finder on my network?

I just bought a new 13" MacBook Air so it has Lion, etc. I just opened Finder a moment ago and on the left under SHARED it showed my desktop PC that's always on, and then I noticed it showed my neighbours MacBook on the list as well. I clicked it and it wanted a password to connect.

I then went to my router config page and viewed attached devices but it only showed my own connected. I then went back to finder and their MacBook had disappeared.

My Bluetooth is on, but does the Finder shared only show computers on my network? Or does it use Bluetooth to find nearby machines as well? As far as I know they don't have my password but my niece when staying with me may have possibly given them the password so I just want to be sure before I change all my network passwords again. Thanks!

Only Machines on the same network will appear in the Shared category, bluetooth has no influence on that AFIK.

Pretty easy to find out for sure, next time you see their MB in the list turn off the Bluetooth and see what happens. Their MB shouldn't disappear from the list.

Then, make Airport stay on but disconnect from the current network like this. There is probably another way but I have't found it

Just copy paste the command to the Terminal app.
Here we make the airport command workable for users and not just the system

sudo ln -s /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport /usr/sbin/airport

And now we can use it, to disconnect from the current network but not turn off the airport card.

airport -z

If you need some assurance that the commands are safe How to spoof your MAC address in Mac OS X

If their MBP disappears from the list when you run the Terminal command, which it should then you know they are on your network.


Of course, the absolute easiest thing to do is to change the router password

If you happen to have the Airport Utility App for the iPhone/iPad then you can see what machines are connected to your network. It allows you to see how many wireless clients are connected, what IPs they are using and what the devices MAC address is.

On that note, I'd set access to your network via MAC addressing. This only allows the devices you approve to be on your network.

EDIT: So does the current version the Airport Extreme. I just figured out how to access the info.