Was it your own or just a discovery? If it's just one you tripped on, I'm going to guess that the owner of the AP or router got smart and secured it. You'd get the signal just fine but, without the security code, you're done for.
I had been picking up an unsecured local wireless network on my Macbook Pro, with no connectivity problems at all. Then I got my desktop G5 going and installed a wireless card to also pick up the signal. For several weeks I was able to connect with both computers with no issues.
Then suddenly a couple days ago, the browser would just hang endlessly searching to connect. On my laptop the signal was noted as strong, and connected. On the G5, the wireless card utility confirmed a strong connection, everything was green light. Still though, on not machines now it just hangs and does not actually receive a web site data.
Why would both machines indicate and confirm a strong connection but in fact it is not connecting? I don't know how to troubleshoot this. The Mac OSX network utility is useless.
Any suggestions would be greatly appreciated. I can also provide more detailed information if necessary. Thanks!!!