What does Rootkit mean?
A rootkit is software used by a hacker to gain constant administrator-level access to a computer or network. A rootkit is typicially installed through a stolen password or by exploiting a system vulnerabilities without the victim's consent or knowledge.
Rootkits primarily aim at user-mode applications, but they also focus on a computer’s hypervisor, the kernel, or even firmware. Rootkits can completely deactivate or destroy the anti-malware software installed in an infected computer, thus making a rootkit attack difficult to track and eliminate. When done well, the intrusion can be carefully concealed so that even system administrators are unaware of it.