|Many people (including myself) have tried to “hide” SSID as a security measure. Unfortunately, efforts to hide SSID ultimately fail and degrade overall WLAN performance.
Lisa Phifer, Configuring service set identifiers
SSIDs are analogous to Windows workgroup names. PCs use those names to browse a network neighborhood and discover others in the same workgroup. When a PC actually tries to access a fileshare, permission is determined by computer name, user name and password. Similarly, stations use SSID to discover APs in the same ESS, but access depends upon other parameters like the station’s address, WEP keys and 802.1X credentials. Access requests must carry the right name, but the workgroup or ESS name is not a password – it identifies the resource to be accessed.