Rootkit - what is rootkit?

Rootkit is a special designed computer programs with unique code created by hacker to conceal their cyber crime activity. Another word to describe rootkit is, a rootkit is computer stealth program created to hide hacker's unauthorized access to a computer. Hacker uses network to gain hidden access to any computer they want, and to cover and to conceal their action, hackers needed rootkit. When a rootkit being installed into a computer, rootkit would be invisible to computer user's eye. Many rootkit were left unquarantined by anti virus programs because these anti virus 'sees' rootkit as clean program.