What is the outcome of a successful man-in-the-middle attack?

A successful man-in-the-middle attack primarily involves the attacker intercepting and potentially altering the communication between two parties without their knowledge. This means that the attacker can eavesdrop on the data being transmitted and may also change the messages being sent or received.

In this scenario, since the attacker is in the middle of the communication channel, they have the ability to manipulate the data, leading to significant security breaches. This could include inserting malicious code into data being sent or changing transaction details to redirect funds, for example.

The other choices do not accurately capture the nature of a man-in-the-middle attack. While data encryption being nullified could be a result of such an attack, it does not encompass the complete outcome of data interception and possible modification, which is a more direct and impactful effect. Rendering network resources inoperable relates more to denial-of-service attacks, and locking users out of their accounts generally pertains to credential theft or exploits unrelated to the interception and modification of data. Thus, the focus of a successful man-in-the-middle attack is on data interception and modification, making this option the most accurate.