"A network-based IDS has little negative affect on overall network performance, and because it is deployed on a single-purpose system, it doesn't adversely affect the performance of any other computer." Pg 34 Krutz: CISSP Prep Guide: Gold Edition.

The correct answer is "Using a hidden, unauthorized network connection to communicate unauthorized information". A Covert Channel is a connection intentionally created to transmit unauthorized information from inside a trusted network to a partner at an outside, untrusted node.
Answer "Socially engineering passwords from an ISP" is called masquerading.

Explanation/Reference:
Explanation:
A session key is a single-use symmetric key that is used to encrypt messages between two users during a single communication session.
If Tanya has a symmetric key she uses to always encrypt messages between Lance and herself, then this symmetric key would not be regenerated or changed. They would use the same key every time they communicated using encryption. However, using the same key repeatedly increases the chances of the key being captured and the secure communication being compromised. If, on the other hand, a new symmetric key were generated each time Lance and Tanya wanted to communicate, it would be used only during their one dialogue and then destroyed. If they wanted to communicate an hour later, a new session key would be created and shared.
A session key provides more protection than static symmetric keys because it is valid for only one session between two computers. If an attacker were able to capture the session key, she would have a very small window of time to use it to try to decrypt messages being passed back and forth.
Incorrect Answers:
A: A secret key is static in nature. It has no fixed lifespan and is used until someone decides to change the key. Session keys are used for single communication sessions so they have a much shorter lifespan.
B: A public key is issued by a CA and typically has a lifespan of one or two years. Session keys are used for single communication sessions so they have a much shorter lifespan.
D: A private key is issued by a CA and typically has a lifespan of one or two years. Session keys are used for single communication sessions so they have a much shorter lifespan.
References:
Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, 2013, pp. 798-799

Section: Software Development Security