A rootkit is a type of malware designed to give hackers access to and control over a target device. The term "rootkit" is a combination of the words "root" and "kit." "Root," "admin," "superuser," or “system admin” are all interchangeable terms for a user account with the admin status of an operating system. Meanwhile, "kit" means a package of software tools. So, a rootkit is a set of tools that gives someone the highest privileges in a system.

Rootkits are generally associated with malware, such as Trojans, worms, and viruses, that conceal their existence and actions from users and other system processes. They can be used to provide continued privileged access to a computer while actively hiding their presence. Rootkits can allow someone to maintain command and control over a computer without the computer user/owner knowing about it.

Rootkits can be used to perform a variety of malicious activities, such as stealing login credentials and financial data, disabling security protocols, logging keystrokes, and more. They can also be used to launch DDoS attacks or send out spam emails, and even disable or remove security software.

Rootkits can be installed on target machines in a number of ways, such as piggybacking with software you trust or with a virus. They can also be employed as a social engineering tactic to trick users into giving the rootkits permission to be installed on their systems, often giving remote cybercriminals administrator access to the system.

To safeguard your system from rootkits, you can ensure it is kept patched against known vulnerabilities, including patches of your OS, applications, and up-to-date virus definitions. You should also avoid accepting files or opening email file attachments from unknown sources and be careful when installing software, carefully reading the end-user license agreements.