Wired Equivalent Privacy or WEP is a security protocol that has been around for quit a while. It has known security issues and is not safe to use any longer. It was superseded first by WPA, then by WPA2 and most recently WPA3. You should always use the most secure option supported by your router. WEP is still an option on many routers for backwards compatibility, but you should avoid it at all costs.
Wired Equivalent Privacy (WEP) was a severely flawed security algorithm for 802.11 wireless networks. Introduced as part of the original IEEE 802.11 standard ratified in 1997, its intention was to provide data confidentiality comparable to that of a traditional wired network. WEP, recognizable by its key of 10 or 26 hexadecimal digits (40 or 104 bits), was at one time widely used, and was often the first security choice presented to users by router configuration tools.Subsequent to a 2001 disclosure of a severe design flaw in the algorithm, WEP was never again secure in practice. In the vast majority of cases, Wi-Fi hardware devices relying on WEP security could not be upgraded to secure operation. Some of the design flaws were addressed in WEP2, but WEP2 also proved insecure, and another generation of hardware could not be upgraded to secure operation.
In 2003, the Wi-Fi Alliance announced that WEP and WEP2 had been superseded by Wi-Fi Protected Access (WPA). In 2004, with the ratification of the full 802.11i standard (i.e. WPA2), the IEEE declared that both WEP-40 and WEP-104 have been deprecated. WPA retained some design characteristics of WEP that remained problematic.
WEP was the only encryption protocol available to 802.11a and 802.11b devices built before the WPA standard, which was available for 802.11g devices. However, some 802.11b devices were later provided with firmware or software updates to enable WPA, and newer devices had it built in.