In cryptography, RC4 (also known as ARC4 or ARCFOUR) is the most wiely-used software stream cipher and is used in popular protocols such as Secure Sockets Layer (SSL) (to protect Internet traffic) and WEP (to secure wireless networks). While remarkable for its simplicity and speed in software, RC4 is vulnerable to attacks when the beginning of the output keystream is not discarded, or a single keystream is used twice; some ways of using RC4 can lead to very insecure cryptosystems such as WEP.