When data is transferred via the airwaves, it can be easily captured using programs downloaded from the Internet. This type of monitoring was expected, and is why WEP security was added to the 802.11 standard. Through the use of WEP, all data can be scrambled to the point where it becomes unreadable. Although WEP will not stop the wanton interception of data, it can stop the casual interpretation of the captured data.
However, there are faults in the implementation of RC4. Specifically, if a hacker can determine what data is being sent before it is encrypted, the captured ciphertext and known plaintext can be XORed together to produce the keystream .