even though there is no WPA/WPSK encoding then your router is still secure.
I have to take issue with that - it is very easy to spoof a MAC address.
Unencrypted network means a wifi packet analyser can read all the packets, then it is trivial to obtain the MAC address and voila - access granted.
Even WEP adds a layer of encryption to break (relatively easily). For proper security, WPA2 is the best - WPA is much better than WEP, but still vulnerable to determined hackers.
SD