MSM422 broadcasting Open SSID

We have 8 MSM422 and I have no problems with the AP perfomance but there is an open SSID from the same network. Let me be more clear:

My SSID is Mynetwork and is secured with password but also I have a open SSID from Mynetwork and it have access to my network files and to the Internet.

I have not found any option where to disable this open SSID.

Anyone have any idea?

Thanks in advance

Luis