You are the senior network administrator for a large corporation. Some new trainees have recently joined the
network security team. You are educating them about denial-of-service (DoS) attacks and the risks posed to a
network by such attacks.
Which three are risks that a DoS attack poses to a network? (Choose three.)

A.
Downtime and productivity loss

B.
Spread of viruses

C.
Revenue loss

D.
Information theft

E.
Spread of spyware

Explanation:
A DoS attack can result in network downtime and loss of productivity, revenue loss, and information theft.
A DoS attack is an attack in which legitimate users are denied access to networks, systems, or resources. The
potential risks posed by a DoS attack are as follows:
Downtime and productivity loss: A DoS attack causes downtime in the network, which ultimately results in
loss of productivity for the organization.
Revenue loss: Organizations that use their Web sites for commerce or vital support services, such as
search engines, can incur large revenue losses.
Information theft: DoS attacks can also be aimed at stealing important and confidential information from a
network.
Malicious competition: An organization might launch DoS attacks against their competitors to damage their
reputation.
A few methods that can help minimize potential risks from DoS attacks are:
Using a firewall, which allows you to block or permit traffic entering into the network, can help to mitigate
DoS attacks.
Computers vulnerable to attacks can be shifted to another location or a more secure LAN.
Intrusion Detection Systems (IDS), such as Network Intrusion Detection Systems (NIDS) and Host Intrusion
Detection Systems (HIDS), can be implemented to detect intrusive network or host activity, such as a DoS
attack, and raise alerts when any such activity is detected.
A DoS attack does not result in the spread of viruses because viruses are not spread by DoS attacks. Viruses
are spread when the network is attacked by a virus or a Trojan horse.
A DoS attack does not result in the spread of spyware. DoS attacks are mainly aimed at exhausting system
resources so that legitimate users are denied access to networks, systems, or resources. Spyware is software
installed on a computer without the knowledge of the user, and it gathers information about a person or
organization. Spyware is generally downloaded through Web sites and e-mail messages.
Objective:
Infrastructure Security
Sub-Objective:
Configure, verify, and troubleshoot basic device hardening

Cisco > Cisco IOS Security Configuration Guide, Release 12.4 > Traffic Filtering, Firewalls, and Virus Detection
> Configuring TCP Intercept (Preventing Denial-of-Service Attacks)