Sometimes you find an open Wi-Fi network but you just could not login, it is because your MAC address is being blocked (MAC address filters) or DHCP is disabled. So you need to find out the MAC address allowed and here is how.
You need two apps here: Network Stumbler and Wildpackets AiroPeek NX. You can always download Network Stumbler from the Internet and it saves a lot of time for you. Make sure your WNIC is supported by Wildpackets AiroPeek NX, and you can see the detailed list at wildpackets.com/support/downloads/drivers, and install the relevant Wildpackets AiroPeek NX WNIC driver.
First, you need to know the SSID, channel, and key (if encrypted) of the targeted WiFi network, and Network Stumbler could of help.
Then, run Wildpackets AiroPeek NX, click New Capture, a Capture window prompts – 802.11. Enter the SSID, channel and the KEY (edit key sets). Now click OK to start capture data packets.
Thirdly, when Wildpackets AiroPeek NX captures some packets, click the Wireless Statistics and you will see the MAC address of the wireless router, as you can see it in Network Stumbler. You will also see another MAC address which is allowed by the Wi-Fi network and this is the MAC address you need.
Finally, you just need to change your MAC address to the above-said address you just found, and now you could login!
Please note I am not here encouraging anyone to hack others WiFi network, just for sharing purpose, and I’ll not bear any responsibility of any consequences incurred thereafter!