Hi Friend,
It depends on how you configure your WLAN/SSID. If it is configured for open authentication then there is no encryption and data is not secured between AP and clients but if you configure your SSID/WLAN and client with encryption technology as WPA1/2 with TKIP/AES you can get a secure communication between client and APs.
See if this link helps you
http://www.cisco.com/univercd/cc/td/doc/product/wireless/control/c44/ccfig41/c41sol.htm#wp1040053
HTH
Ankur
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