Several users’ computers are no longer responding normally and sending out spam email to the users’ entire contact list. This is an example of which of the
following?

A.
Trojan virus

B.
Botnet

C.
Worm outbreak

D.
Logic bomb

Explanation:
A worm is similar to a virus but is typically less malicious. A virus will usually cause damage to the system or files whereas a worm will usually just spread itself
either using the network or by sending emails.
A computer worm is a standalone malware computer program that replicates itself in order to spread to other computers. Often, it uses a computer network to
spread itself, relying on security failures on the target computer to access it. Unlike a computer virus, it does not need to attach itself to an existing program. Worms
almost always cause at least some harm to the network, even if only by consuming bandwidth, whereas viruses almost always corrupt or modify files on a targeted
computer.
Incorrect Answers:
A: In computers, a Trojan horse is a program in which malicious or harmful code is contained inside apparently harmless programming or data in such a way that it
can get control and do its chosen form of damage, such as ruining the file allocation table on your hard disk. In one celebrated case, a Trojan horse was a program
that was supposed to find and destroy computer viruses. A Trojan horse may be widely redistributed as part of a computer virus. In this question, no actual damage
was done to the computers. Emails were sent to spread the worm. Therefore, this answer is incorrect.
B: A botnet is a collection of Internet-connected programs communicating with other similar programs in order to perform tasks. This can be as mundane as
keeping control of an Internet Relay Chat (IRC) channel, or it could be used to send spam email or participate in distributed denial-of-service attacks. The word
botnet is a combination of the words robot and network. The term is usually used with a negative or malicious connotation. Computers can be co-opted into a
botnet when they execute malicious software. This can be accomplished by luring users into making a drive-by download, exploiting web browser vulnerabilities, or
by tricking the user into running a Trojan horse program, which may come from an email attachment. This malware will typically install modules that allow the
computer to be commanded and controlled by the botnet’s operator. Many computer users are unaware that their computer is infected with bots. Depending on how
it is written, a Trojan may then delete itself, or may remain present to update and maintain the modules. Botnets can be used to send spam emails but this would
be done by someone controlling the computers to target an individual or entity with the spam. A worm would use its own programming to send emails to everyone
in a contact list with the aim of spreading itself. Therefore, this answer is incorrect.

D: A logic bomb is a piece of code intentionally inserted into a software system that will set off a malicious function when specified conditions are met. For example,
a programmer may hide a piece of code that starts deleting files should they ever be terminated from the company. Software that is inherently malicious, such as
viruses and worms, often contain logic bombs that execute a certain payload at a pre-defined time or when some other condition is met. This technique can be
used by a virus or worm to gain momentum and spread before being noticed. Some viruses attack their host systems on specific dates, such as Friday the 13th or
April Fool’s Day. Trojans that activate on certain dates are often called “time bombs”. To be considered a logic bomb, the payload should be unwanted and
unknown to the user of the software. As an example, trial programs with code that disables certain functionality after a set time are not normally regarded as logic
bombs. A logic bomb may contain a worm but it is the worm that is sending the emails. Therefore, this answer is incorrect.

http://en.wikipedia.org/wiki/Computer_worm
http://searchsecurity.techtarget.com/definition/Trojan-horse http://en.wikipedia.org/wiki/Botnet
http://en.wikipedia.org/wiki/Logic_bomb