With a "doorknob-rattler" type of attacker (someone randomly trying WEP keys) either level will give you better protection than not enabling WEP, provided you choose a non-obvious WEP key. If your WLAN is targeted by a more sophisticated user, using tools such as AirSnort or WEPCrack , then your WLAN could be cracked in as little as a few hours, but more likely a day or so, regardless of WEP mode used.