The following is missing for the question to be complete:
- Rootkit
- Backdoor
- Wrapper
- Shield
Answer: Rootkit
Explanation: Rootkit is a set of software, such as malicious software, created by an attacker to allow access to a computer, that is, its software, and thus take malicious action against the attacked computer, while hiding the presence of malicious software. This is, of course, undertaken by one who does not have access to the computer he or she wants to attack, therefore is not authorised to access it. This malware contains a spectrum of different tools and is used by attackers to, say, neutralise antiviruses on an attacked computer and the like. Using a rootkit, an attacker gains access to a computer that is the same as an administrative one, and is installed using a hacked password or other hacking method without the knowledge of the victim.
