Aircrack-ng is a complete suite of tools to assess WiFi network security.
The default cracking method of Aircrack-ng is PTW, but Aircrack-ng can also use the FMS/KoreK method, which incorporates various statistical attacks to discover the WEP key and uses these in combination with brute forcing.

References: http://www.aircrack-ng.org/doku.php?id=aircrack-ng

In a split DNS infrastructure, you create two zones for the same domain, one to be used by the internal network, the other used by the external network. Split DNS directs internal hosts to an internal domain name server for name resolution and external hosts are directed to an external domain name server for name resolution.

References: http://www.webopedia.com/TERM/S/split_DNS.html

An attacker uses a TCP XMAS scan to determine if ports are closed on the target machine. This scan type is accomplished by sending TCP segments with the all flags sent in the packet header, generating packets that are illegal based on RFC 793. The RFC 793 expected behavior is that any TCP segment with an out-of-state Flag sent to an open port is discarded, whereas segments with out-of-state flags sent to closed ports should be handled with a RST in response. This behavior should allow an attacker to scan for closed ports by sending certain types of rule-breaking packets (out of sync or disallowed by the TCB) and detect closed ports via RST packets.

References: https://capec.mitre.org/data/definitions/303.html

A DMZ or demilitarized zone (sometimes referred to as a perimeter network) is a physical or logical subnetwork that contains and exposes an organization’s external-facing services to a larger and untrusted network, usually the Internet. The purpose of a DMZ is
to add an additional layer of security to an organization’s local area network (LAN); an external network node only has direct access to equipment in the DMZ, rather than any other part of the network.

References: https://en.wikipedia.org/wiki/DMZ_(computing)

Wireshark is a Free and open source packet analyzer. It is used for network troubleshooting, analysis, software and communications protocol development, and education.
Incorrect Answers:

B: Nessus is an open-source network vulnerability scanner that uses the Common Vulnerabilities and Exposures architecture for easy cross-linking between compliant security tools.
C: Netcat (often abbreviated to nc) is a computer networking utility for reading from and writing to network connections using TCP or UDP.
D: Netstat provides network statistics.
References: https://en.wikipedia.org/wiki/Wireshark

By setting up an email address for your users to forward any suspicious email to, the emails can be automatically scanned and replied to, with security incidents created to follow up on any emails with attached malware or links to known bad websites.
References: https://docs.servicenow.com/bundle/helsinki-security-management/page/product/threat-intelligence/task/t_ConfigureScanEmailInboundAction.html

Shellshock, also known as Bashdoor, is a family of security bugs in the widely used Unix Bash shell, the first of which was disclosed on 24 September 2014.
References: https://en.wikipedia.org/wiki/Shellshock_(software_bug)

Cross-site request forgery, also known as one-click attack or session riding and abbreviated as CSRF (sometimes pronounced sea-surf) or XSRF, is a type of malicious exploit of a website where unauthorized commands are transmitted from a user that the website trusts.
Different HTTP request methods, such as GET and POST, have different level of susceptibility to CSRF attacks and require different levels of protection due to their different handling by web browsers.

References: https://en.wikipedia.org/wiki/Cross-site_request_forgery

Stuxnet is a malicious computer worm believed to be a jointly built American-Israeli cyber weapon. Exploiting four zero-day flaws, Stuxnet functions by targeting machines using the Microsoft Windows operating system and networks, then seeking out Siemens Step7 software.

References: https://en.wikipedia.org/wiki/Stuxnet

Nessus is an open-source network vulnerability scanner that uses the Common Vulnerabilities and Exposures architecture for easy cross-linking between compliant security tools.
The Nessus server is currently available for Unix, Linux and FreeBSD. The client is available for Unix-or Windows-based operating systems.
Note: Significant capabilities of Nessus include:
Compatibility with computers and servers of all sizes.

Detection of security holes in local or remote hosts.
Detection of missing security updates and patches.
Simulated attacks to pinpoint vulnerabilities.
Execution of security tests in a contained environment.
Scheduled security audits.
References: http://searchnetworking.techtarget.com/definition/Nessus