From this report :
Contrary to a common belief that the SSID is a WLAN security feature and its exposure a security risk, the SSID is nothing more than a wireless-space group label. It cannot be successfully hidden. Attempts to hide it will not only fail, but will negatively impact WLAN performance, and may result in additional exposure of the SSID to passive scanning.
I can tell you from bitter experience that this is true. This link was brought to my attention a couple of months ago by Mark Leyden when we were trying to debug some mysterious WLAN problems in work. We had been using SSID hiding, and some machines were continually disconnecting and reconnecting to the WLAN. We turned on broadcasting of the SSID and most of the problems just went away.
People in work still come up to me and say “I can see the SSID of the work WLAN – is that such a good idea?” and I have to keep explaining.
Later, I discovered that IBM T60p laptops wouldn’t connect to my home WLAN, even though my trusty iBook never had a problem (my trusty iBook never has a problem). I turned on SSID broadcast, and it worked.
I thought at the time that maybe this was causing my mysterious Wii network connection failure, but didn’t test it (I haven’t used the Wii in forever). Today I did. It works.
Today’s moral – a network with a hidden SSID is a broken network. End of story.