Man in the Middle Attack

A man-in-the-middle attack is a cyber-attack in which an attacker intercepts communications between two parties without either party knowing about it. So, for example, when Alice sends a message to Bob, the attacker intercepts it before it gets to Bob. The attacker can then read the message and even send a different message along to Bob. Meanwhile, Bob and Alice think they are simply talking to each other and are unaware that someone is listening to and possibly modifying the conversation.