The word Rootkit has been derived by two words. The word ‘root’ which means total control over the system administrator rights by bypassing the authentication process.
And ‘kit’ means the set of tools like software applications and packages to undergo this intrusion for privileged access.
Once the intruder gets total control over the system, he or she can do anything. If hacker hacks your computer and gets ‘rootkit’ control of it. That means the hacker has bypassed all of the defense systems and gets control like a admin.