>почитайте что такое руткит http://ru.wikipedia.org/wiki/%D0%A0%D1%8...

http://en.wikipedia.org/wiki/Rootkit

A rootkit is a software or hardware device designed to gain administrator-level control over a computer system without being detected. Although rootkits can serve a variety of ends, they have gained notoriety as malware, appropriating computing resources without the knowledge of the administrators or users of affected systems. Rootkits can target the BIOS, hypervisor, boot loader, kernel or less commonly, libraries or applications.

The term rootkit is a concatenation of the administrative account in (primarily) Unix operating systems (root user account) and the word "kit", which refers to the software components that implement the tool.

Т.е. именно to gain - получить рутовый уровень доступа.