An initialization vector (IV) attack is an attack on wireless networks. It modifies the IV of an encrypted wireless packet during transmission. Once an attacker learns the plaintext of one packet, the attacker can compute the RC4 key stream generated by the IV used. This key stream can then be used to decrypt all other packets that use the same IV. Since there is only a small set of possible initialization vectors, attackers can eventually build a decryption table to decrypt every packet sent over that wireless connection.