You want to perform an active session hijack against Secure Inc. You have found a target that allows Telnet session. You have also searched an active session due to the high level of traffic on the ne

Sniffing is a prior step used to discover active sessions - the question states the attacker has already found an active session, so sniffing is no longer the next required action.

TCP sessions are tracked by sequence and acknowledgment numbers; to inject a forged packet that the server accepts as legitimate, the attacker must determine the current sequence number of the ongoing session. Guessing or predicting the sequence number is the critical next step after locating an active session, enabling the attacker to craft a packet that fits the expected stream and execute commands as the hijacked user.

Brutus is a password brute-force tool; cracking the Telnet password is an authentication attack, not an active session hijack of an already-established session.

Changing a MAC address with macof (or macoff) is relevant to MAC flooding or ARP-level attacks, not to TCP sequence number prediction required for session hijacking.