Non$-$Repudiation

a$)$ is a network security appliance that monitors network and system activities to reveal possible intrusions. In addition to detecting intrustions, it can also prevent them by sending alarms, block malicious network messages $($and their responses$)$ so they do not reach their destination, and reset network connections.

b$)$ is a mechanism to ensure that individuals cannot deny their actions. Examples include ensuring that users who spend money cannot deny that they really did authorize a transaction, or authors who edit a text cannot pretend that the change was theirs.

$q,$ c$)$ involves full$-$time monitoring tools that search for patterns in network traffic to identify intruders. IDS was cutting edge a decade ago, but has now evolved into Intrustion Detection and Prevention Systems.

$q,$ d$)$ involves small electronic devices that change user passwords automatically.

e$)$ A masquerading attack that combines spam with spoofing.