A program has been discovered that infects a critical Windows system executable and stays dormant in memory. When a Windows mobile phone is connected to
the host, the program infects the phone’s boot loader and continues to target additional Windows PCs or phones. Which of the following malware categories BEST
describes this program?

A.
Zero-day

B.
Trojan

C.
Virus

D.
Rootkit

Explanation:
A computer virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes. Viruses can also replicate
themselves. All computer viruses are man-made. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a
simple virus is dangerous because it will quickly use all available memory and bring the system to a halt. An even more dangerous type of virus is one capable of
transmitting itself across networks and bypassing security systems. Some people distinguish between general viruses and worms. A worm is a special type of virus
that can replicate itself and use memory, but cannot attach itself to other programs.
Incorrect Answers:
A: A zero day vulnerability refers to a hole in software that is unknown to the vendor. This security hole is then exploited by hackers before the vendor becomes
aware and hurries to fix it –this exploit is called a zero day attack. Uses of zero day attacks can include infiltrating malware, spyware or allowing unwanted access
to user information. The term “zero day” refers to the unknown nature of the hole to those outside of the hackers, specifically, the developers. Once the vulnerability
becomes known, a race begins for the developer, who must protect users. A zero-day vulnerability is not described in this question. Therefore, this answer is
incorrect.

B: In computers, a Trojan 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 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. A Trojan is not what is being described in
this question.
A Trojan is not what is described in this question. Therefore, this answer is incorrect.
D: A rootkit is a stealthy type of software, typically malicious, designed to hide the existence of certain processes or programs from normal methods of detection
and enable continued privileged access to a computer. A rootkit is not what is described in this question. Therefore, this answer is incorrect.

http://www.webopedia.com/TERM/V/virus.html
http://www.pctools.com/security-news/zero-day-vulnerability/