Answer:
A man-in-the-middle attack.
The attacker is not actually on the network, but instead pretends to be a trusted resource (usually an Internet connection) by intercepting all traffic going to or from that server or service. This means they can read or modify the traffic before it reaches its destination. For example, if a website you are visiting sends your password to another site in cleartext, a man-in-the-middle could intercept this packet and read your password.
Step-by-step explanation:
My own original answer.