RC4 is a stream cipher designed by Ron Rivest in 1987. It encrypts data by generating a pseudorandom stream of bits, which is then combined with the plaintext to produce ciphertext. RC4 is known for its simplicity and speed, making it popular in various applications, including SSL/TLS for secure web communications. Despite its initial popularity, vulnerabilities have been discovered in RC4, leading to security concerns. As a result, many organizations have moved away from using RC4 in favor of more secure algorithms, such as AES (Advanced Encryption Standard). This shift reflects the ongoing evolution of cryptographic practices to enhance data security.