Original: Finally in 2004, with the ratification of the full 802.11i standard (a.k.a. WPA2), the IEEE declared that both WEP-40 and WEP-104 "have been deprecated as they fail to meet their security goals".
Simplified: It was part of the full 802.11i standard (also known as WPA2), the IEEE declared that both WEP-40 and WEP-104 "have been deprecated as they fail to meet their security goals".