Which of the following describes an attack that monitors packet data and attempts to modify it?

The Man-in-the-Middle Attack is characterized by an attacker intercepting communication between two parties. In this scenario, the attacker sits between the sender and receiver, monitoring the packet data being transmitted. This enables the attacker to not only observe the communication but also to modify it in transit without the knowledge of either party. Typically, the attacker can alter the data being sent, injecting malicious content or changing the information to exploit vulnerabilities or compromise security.

This type of attack is particularly dangerous in scenarios where sensitive information is being exchanged, such as login credentials, financial information, or personal data. The attacker's ability to modify data can lead to unauthorized access or manipulation of transactions.

Other types of attacks listed, such as a Replay Attack, primarily involve the repetition of previously captured valid data transmissions without modification. Denial of Service Attacks focus on overwhelming a target to make services unavailable, and Spear Phishing Attacks involve targeted attempts to deceive individuals into revealing personal information but do not typically involve real-time communication interception and modification.