Which of the following defines a rootkit?

a. It is the act of fraudulently using email to try to get the recipient to reveal personal data by sending legitimate-looking emails urging the recipient to take action to avoid a negative consequence or to receive a reward.
b. It is the unintended release of sensitive data by unauthorized individuals.
c. It is the abuse of email systems to send unsolicited email to large numbers of people.
d. It is a set of programs that enables its user to gain administrator-level access to a computer without the end user’s consent or knowledge.

d. It is a set of programs that enables its user to gain administrator-level access to a computer without the end user’s consent or knowledge.
A rootkit is a set of programs that enables its user to gain administrator-level access to a computer without the end user’s consent or knowledge. Once installed, the attacker can gain full control of the system and even obscure the presence of the rootkit from legitimate system administrators.