"Unknown" security?

["Miner, Jonathan W \(US SSA\)" <jonathan w miner baesystems com>]

When I look at the "Connection Information" under the applet, my hardwired ethernet connection is listed as having "unknown" security.  If I connect to an open wireless network, its security is shown as "none".  Can someone explain the difference between "none" and "unknown"?

Isn't it true that you could apply MAC filtering in either case, and NetworkManager wouldn't know that filtering was being applied? 

Thanks