What does "session hijacking" refer to in the context of network security?

Session hijacking refers specifically to the unauthorized takeover of a user session after a user has authenticated with a service. This typically involves an attacker gaining control over a legitimate user's session by intercepting or predicting the session token, thereby impersonating that user on the network.

When focusing on why the chosen answer is accurate, it highlights the act of altering an active TCP connection. This alteration enables an attacker to send or receive messages as if they were the legitimate user, which is the fundamental concept behind session hijacking. In the process, the legitimate user's session is compromised, allowing the attacker to effectively take over the interactions.

The other options, while related to network security, do not accurately define session hijacking. For instance, unauthorized access to a secured file or capturing network traffic do not specifically involve the manipulation of an established session. Furthermore, injecting malware into a session is a different attack vector, focusing on the insertion of malicious code rather than the hijacking of an existing communication session.