wpa and no broadcast ssid

reason: hide the ap

You can't really hide the AP. You can make it more difficult for normal connections. SSID hiding provides no security advantage.

Lookup "active scanning"; you can't really hide the AP.

Can U send me a link about the 'active scanning' ? You say that a user could discover my wifi-network if I don't broadcast the ssid ?

Look up "kismet". Install it. Turn off your normal wifi initialization (eg. "ifdown ath0" in linux). Then run kismet. Notice all the SSID="" BSSID=11:22:33:44:55 entries. The SSID won't be known until some client transmits it. Once a client packet contains both the previously unknow SSID and already known BSSID, the gig will be up. Anyone that was paying attention will know your SSID. What have you bought yourself? A few extra minutes for all the pain of your laptop sending probe packets for your AP continuously instead of just passively scanning? Personally, I don't want my laptop transmitting more than necessary and running down the batteries which are already much too small.

In general you'd do well to ignore advice from any web page that still gives instructions for setting up wep. At best its back from the days when wep was still treated as a somewhat worthwhile method of securing one's wifi. It really should be treated more like a rot-13 these days. It keeps you from inadvertently seeing something you really didn't want to see.

-wolfgang