$27$ From a security perspective, a$($n$)\_\_\_\_\_\_\_\_\_\_\_$ masks the identity of a client and limits the usefulness of network sniffing.

a$)$ router

b$)$ proxy server

c$)$ switch

d$)$ firewall

$28.$ Which of the following audit tools is used to identify rogue systems and services?

a$)$ checklists

b$)$ integrity checking

c$)$ vulnerability scanners

d$)$ IP$/$port scanners

$29.$ A common technique often used in high security environments to establish an unalterable paper trail for $log$ files is called$\_\_\_\_\_\_\_\_\_\_\_\_.$

a$)$ remote logging

b$)$ printer logging

c$)$ security logging

d$)$ cryptographic technology